I think it's OK to have a liquor cabinet, but I think it's wrong (or at the ver least unnecessary) to lock it.
Your children should know what they can't do and why (like using your or any liquors for several reasons), but they should also know that you trust them.
Putting a simple barrier is enough to make the intention clear. Putting a strong barrier makes them want to break it. They can't trust you if you don't trust them and take arbitrary decisions. You can't expect them to be rational and demand from them that they use critical thinking and reason before taking action if your own resolutins are not based on substantiated and reasoned arguments but are arbitrary rules.
And in response to someone mentioning it prevents peer pressure in the case of an home-party and their friends wanting to raid their cabinets... If you can't trust your kids to tell you the truth about who did, then there's a problem somewhere else. If they lie to you, it's either because they're scared of disproportionate consequences (because they actually did do it or didn't prevent it), or because they are afraid you won't believe them, or because they're afraid your reaction will be unjust in other ways.
If by any misfortune that boat has already sailed for your kids anyways, then yeah, you might resort to locking stuff away. But it won't do anything to fix the problems.
For the record, maybe I appear quite liberal on this, but underage drinking isn't such a disproportionate issue in my country. The legal age for buying alcohol yourself is 18, though it's very common for kids to consume long before that, in reasonable volumes on exceptional occasions, and in probably fairly excessive volumes as you can imagine when unsupervised. However, we don't have, at least in our area, proven damaging and long-lasting effects. Problems are the exception, not the norm.