Hey there, I am new to itch.io, and enjoyed it so far, but:

Are undoubtedly sexist games that implement objectifying and
rather pornographic real-life pictures of women in line with the ideas of itch.io?
Are sexist public profile messageboard conversations "discussing" those games in line with it?

I read, that one may report sites at the bottom, but there is no report button on one particular site for instance. 
Just wondering.

Excuse me, report "sites"? What sites? If you mean a particular game or forum topic, please link to it so we can investigate. Thanks.

Edit: to answer your question, I'd have to ask about any official policy, but far as I can tell we try not to be arbiters of taste. Hope this helps.