Do most denominations of Christianity consider them to be true stories
or do they consider them to be myths?
Stating with certainty the position of "most denominatios of Christianity" on any issue would require a huge amount of survey work, because there are thousands of denominations. Therefore that question, as stated, cannot be answered.
Now, speaking individually as a Roman Catholic, I can state that the Roman Catholic Church considers all stories in the New Testament factually true, allowing for some simplification of concrete details and some grouping of events and discourses by the evangelists, because they wrote for a catechetical purpose, not for recording history in the modern scientific sense of the term.
If they consider them to be true stories, how do they explain away the
lack of evidence? Something like the Massacre of the Innocents or a
zombie apocalypse would certainly be noted by non-Christian sources,
wouldn't it?
Regarding the Massacre of the Innocents, what kind of evidence would you expect of Herod sending a bunch of trusted soldiers to kill maybe 10 babies in Bethlehem and around? Do you expect Herod to put the order in writing? Or to send a letter to Augustus requesting permission?
What we do know from recorded history is that the order was entirely in line with Herod's character. The guy accused his own sons Alexander and Aristobulus of high treason in 8 BC and had them executed in 7 BC, and then did the same to another son, Antipater, in 5 BC and 4 BC [1]. Moreover, Josephus wrote that when he felt his own death was imminent he had all principal men of Judean society gathered in the hyppodrome to have them all killed after his death, so that there would be great mourning in Judea! [2]
Regarding the resurrection of many saints at the time of Jesus' death according to Mt 27:52-53, a simple hypothesis can account for the complete silence about this event in non-Christian sources: the saints raised in Mt 27:52 were precisely the children murdered in Mt 2:16.
First, this hypothesis explains the term "the Holy City" in Mt 27:53, which, if understood as referring to physical Jerusalem, would carry a strong cognitive dissonance. Would precisely Matthew, who a few chapters before had quoted Jesus saying "Jerusalem, Jerusalem, who kills the prophets and stones those who are sent to her!" (Mt 23:37) and a few verses before had narrated that "All the people answered, “His blood be on us and on our children!”" (Mt 27:25), refer to Jerusalem as "the Holy City"??? It is far more plausible that Matthew is referring here to the New Jerusalem, the spiritual Jerusalem, the Church: the raised saints appeared, or better said manifested, disclosed, revealed themselves as resurrected (*), to members of the Church.
Centrally to the question at hand, this hypothesis explains the total absence of social impact in Jerusalem out of that resurrection of "many" (maybe 10, certainly no more than 20) saints: given that they had died 35 years ago while being less than 2 years old, and that they had been raised as adults, any inhabitant of Jerusalem that crossed ways with one of them would have no idea at all of whom he was, even less of the fact that he had been raised from the dead, and would simply take him as just another Jew that had come from far away to Jerusalem for the Passover. Only those members of the Church to whom these raised saints manifested, disclosed, revealed themselves as such, i.e. as resurrected (*), could come to know what had really happened.
(*) The word in Mt 27:53 usually translated as "appeared" is enephanisthēsan, 3rd person plural of the aorist indicative passive tense of the verb emphanizō, which appears 10 times in the NT, with the following meanings in the other passages:
Jn 14:21-22: manifest, disclose, reveal (oneself)
Act 23:15: give notice, make a report, notify
Act 23:22: report, notify
Act 24:1; 25:2; 25:15: present (a case against X), inform (Y about X)
Heb 9:24: appear
Heb 11:14: make manifest, make it clear
From these occurrences, it is clear that the expression in Mt 27:53 can be plausibly understood as meaning that the raised saints manifested, disclosed, revealed themselves as resurrected to many, that they notified many about their resurrection.
It is also clear that these "many" to whom the raised saints manifested themselves as such were exclusively members of the initial community of disciples of Jesus, because they were the only ones who could believe their testimony. Just think of the reaction of an inhabitant of Jerusalem in 30 AD (or of anyone at any place in any time) if a stranger approaches him saying: "Hi, I have been dead for the last 35 years and have just been raised from the dead. Would you be so kind as to provide me with lodging and food for a while?"
If anyone wants to know whether and how this hypothesis makes theological sense, see [3].
References
[1] https://en.wikipedia.org/wiki/Herod_the_Great#Last_decade_BCE
[2] Josephus, "The Antiquities of the Jews", Book XVII, Chapter 6.
https://gutenberg.org/cache/epub/2848/pg2848-images.html#link172HCH0006
"and having no longer the least hopes of recovering, he gave order that every soldier should be paid fifty drachmae; and he also gave a great deal to their commanders, and to his friends, and came again to Jericho, where he grew so choleric, that it brought him to do all things like a madman; and though he were near his death, he contrived the following wicked designs. He commanded that all the principal men of the entire Jewish nation, wheresoever they lived, should be called to him. Accordingly, they were a great number that came, because the whole nation was called, and all men heard of this call, and death was the penalty of such as should despise the epistles that were sent to call them. And now the king was in a wild rage against them all, the innocent as well as those that had afforded ground for accusations; and when they were come, he ordered them to be all shut up in the hyppodrome, 9 and sent for his sister Salome, and her husband Alexas, and spake thus to them: "I shall die in a little time, so great are my pains; which death ought to be cheerfully borne, and to be welcomed by all men; but what principally troubles me is this, that I shall die without being lamented, and without such mourning as men usually expect at a king's death." For that he was not unacquainted with the temper of the Jews, that his death would be a thing very desirable, and exceedingly acceptable to them, because during his lifetime they were ready to revolt from him, and to abuse the donations he had dedicated to God that it therefore was their business to resolve to afford him some alleviation of his great sorrows on this occasion; for that if they do not refuse him their consent in what he desires, he shall have a great mourning at his funeral, and such as never had any king before him; for then the whole nation would mourn from their very soul, which otherwise would be done in sport and mockery only. He desired therefore, that as soon as they see he hath given up the ghost, they shall place soldiers round the hippodrome, while they do not know that he is dead; and that they shall not declare his death to the multitude till this is done, but that they shall give orders to have those that are in custody shot with their darts; and that this slaughter of them all will cause that he shall not miss to rejoice on a double account; that as he is dying, they will make him secure that his will shall be executed in what he charges them to do; and that he shall have the honor of a memorable mourning at his funeral. So he deplored his condition, with tears in his eyes, and obtested them by the kindness due from them, as of his kindred, and by the faith they owed to God, and begged of them that they would not hinder him of this honorable mourning at his funeral. So they promised him not to transgress his commands.
- Now any one may easily discover the temper of this man's mind, which not only took pleasure in doing what he had done formerly against his relations, out of the love of life, but by those commands of his which savored of no humanity; since he took care, when he was departing out of this life, that the whole nation should be put into mourning, and indeed made desolate of their dearest kindred, when he gave order that one out of every family should be slain, although they had done nothing that was unjust, or that was against him, nor were they accused of any other crimes; while it is usual for those who have any regard to virtue to lay aside their hatred at such a time, even with respect to those they justly esteemed their enemies."
[3] https://www.academia.edu/34622725/
