If kids are having good, clean fun, then I support them 100%. Adults reliving childhood? I support that 100% too. Take your joy where you can get it. Leave the judgement for places in the world that actually need it (where we can help and make a difference).
As far as snarking at teens and making comments insinuating it should be their last year, please reconsider saying something that could make them feel ashamed of a wholesome and fun activity. And there's nothing wrong with being a "geek"--silicon valley's inhabitants are living proof of that. There's plenty of time in life for partying, nerd or not, and scary movies are any day of the month of October, not just on Halloween.