Binks. It's not about people being scared of 'extreme' sex. It's about people being concerned about 'extreme' sex being portrayed as the 'norm' and not therefore 'extreme' at all, but just 'what you do'.
Now, you may love a bit of violent sex. Marvelous, knock yourself out (or have your DP do it for you, whatevs) but you have to admit, that sort of sex is not the norm and not for everyone.
It needs to be conducted in a relationship with an amount of trust IMO and an understanding of the limits of the other person.
Porn is often a young persons first introduction to sex. (I am not saying this is right or should happen, but it does)
Due to the internet, we've moved an awful long way from finding a Hustler magazine in the bushes. If Sascha Grays films form your image of sex, you may feel that sex is standard and feel pressurised into replicating the sex in those films. Even though you may not enjoy it, feel comfortable, understand it, or be with a partner with whom it is safe to explore that sort of sex. Which isn't good.
I may enjoy my DH choking me till I pass out (I said may - it's an example). That's fine. Because I trust him, because I enjoy it, because I consent, because he knows my limits, blah blah - but importantly, because I am acting in as close to a bubble as I can get. The only person that impacts on is my DH, and assuming we don't split up and he doesn't cheat, it's had a minimal impact on other women. Hence, no one cares what you, or I or the postman get up to in bed (usual caveats about consenting adult), because its impact on the rest of society is pretty negligible.
Oh, and because other peoples sex lives are boring. Even yours - promise.
Porn is rather different as it does have an impact on society and on sexual culture. Therefore, people care about it and many people feel the 'extremes' of sex should remain just that and should not be presented as the mainstream, which creates a pressure for people to participate regardless of whether they enjoy it, want to or are in a safe position to do so. This is particularly so when we live in a world where porn is so easily accessible and so often accessed by children.
A while ago you'd would have had to go to a specialist shop to get hold of extreme porn. It would have been a mission for an adult and pretty near impossible for a child. So the impact on society is much smaller. Now you just click a button. Or read about it in Elle magazine.