That would limit the total addressable market from 100% to, say, 1-5%. Statistically, legally, socially, that's not "defeating the purpose", that's "job done", instead.

Most people here should be engineers or at least analytical. No solution is 100%.

Checking ID to prevent the sale of tobacco to children may not prevent them from ever smoking but is considered better than nothing. This product would be sold in exactly the same manner at the same locations.

Prevents kids from stumbling onto it by accident at very least.

Most minors don't smoke or drink, even though straw purchases of booze and cigs are a thing. Social media is even more amenable to this type of gatekeeping because if most of your social circle isn't on it, you have no reason to be there either.