In this case I would argue that on the web you're unnaturally often confronted with sexual content, much more than you would be in reality.
However I agree with you, this is kind of a delicate topic. The passive "I want to avoid" can easily be turned into an active "woman should not be allowed to wear short skirts because that is sexually attractive to me" and this is very dangerous thinking. It is diametrical to my own beliefs as I think nobody is allowed to tell anybody else how to dress in public. Your nudity example is of cause pretty extreme.
I am a feminist and an ally, but I am also a man and I struggle with the topic in general. I am easily aroused from visual stimuli, it's nothing I can prevent. For sure I keep this in my head and I would never stare, catcall or whatever but I sometimes which I wouldn't be confronted with these stimuli in the outside world, it is distracting.
I haven't thought this through completely and I find it a very difficult topic to talk about. There are two sides fighting - my liberal world view and my desire to normalize nudity versus a hypersexualized web and pop culture; and I feel avoiding this stuff and blocking NSFW helps me to desensitize, if that makes sense to you.