yitay:First, even if there is an issur with a woman having lewd thoughts a man who is an ervah, that doesn’t mean that she is as likely to have those lewd thoughts simply by looking at men, as men are by looking at women. I’m not saying they aren’t, but if you want to make issurim you have to prove it.
I was clear with my words to not use the word assur. I said there “can be an issur de’oraysa of histaklus” and that I would be “careful not to mattir”. I said “can be assur” because
a) It all depends on the woman’s intentions.
b) I also think that there may be others that are cholek, for example the Sefer Hachinuch’s pshat on Lo Sassuru is a da’as yochid. (Although, there are other shittos that assur for other reasons). However, a Rishon is a Rishon, and I wouldn’t be so quick to matir against him either.
Second, the three sources you cite are not generally regarded as the most authoritative sefarim when it comes to halacha.
That is all I found. If you can find me something else, great. However, some of those sources learnt that histaklus (for pleasure) is the same issur as men looking at women (for pleasure), which there is plenty of sources for. I’m sure there are differences, because a woman looking at a not-fully dressed man is not looking at an Erva, whereby vice-versa most definitely is.