Since many of you have a hard time grasping this concept, maybe a first person account will help.
When I was in eighth grade, I went to a friend’s house who had unfiltered internet, and we found things that have changed both of our lives forever. I’m a regular, even above average trains guy, so it wasn’t because I was going off our trying to do bad things, kids just that I was an innocent kid who saw things I wish I didn’t know existed.
Most normal, healthy males have taava, and you see from all the halochos and gedarim how concerned Hashem and Chazal are about people being nichshal. Even if a person can usually be fine, if it’s accessible, all it takes is ONE moment of weakness, and he can ruin his life. And even if there’s someone who can always control himself, he may see something inadvertently. And anyway, the Mishna says, “al taamin biatzmecha ad yom moscha”. The threat is real, don’t play games. And if not for you, for your kids or anyone else who may use your computer.