I played Doom as a toddler, in my dad's lap. I had early and unfettered access to all kinds of porn. I listened to insanely homophobic, sexist, and generally antisocial music (Eminem, D12).
If you wiped my brain and gave me amnesia and asked me if those things will mess a kid up, I'd say yeah -- how couldn't they?!
It turns out they had no negative effect on me that I can notice; they were just fun. As an adult, I don't do drugs, I've got all the fashionably cosmopolitan social views, etc. :p It's anecdata, but I think the biggest factors for how kids end up are "did you come out screwed up already" and "are your parents emotionally and financially-supportive while vaguely indicating the glide path they think you should follow, with stuff like off-handedly remarking on how racism is pretty bad at some point and generally forcing you to do well in school and putting you through college".
Honestly, this was not different in my youth. When we found access to the internet, we of course looked for weird stuff (for those who remember: for example rotten.com; I was rather disturbed by it and learned my lesson that you shouldn't click on every link that you see on websites).
I can tell you how this transformed me: if you have seen the early free spirit of the early web in your formative years, you become deeply suspicious of the political attempts to censor the internet - for example to "protect the children". This is what the authorities really fear: that people don't believe that this is all for their best.