Okay, I'm going to try and answer this from the perspective of someone who doesn't hate Nadia, but has disliked a lot of her behaviour; has some compassion for her current situation, but also thinks she needs to take responsibilty for her own actions rather than blame it all on others/the BB edit; and incidentally from someone who has close first hand-experiences of gender dysphoria affecting people v close to me:
 Why, if all the Nadia "hate" has nothing to do with her gender reassignment WHY in NEARLY EVERY thread about Nadia is her gender dragged up and ripped to shreds (by the same forum members i may add) WHY is it even mentioned? 
'Cos it's human nature? Same way as in just about every thread where people were expressing dislike for Josie her weight was mentioned, or in just about every thread about Steve his disability was mentioned etc. etc. That doesn't make it right but that is, imo, part of the explanation, however I think it's much more complicated than that:  Nadia's 'mission' in BB5 was to be accepted as a woman, it was, I believe why so many warmed to her, empathised with her and most probably was a big part of why she went on to win the show. It was also, I assume, one of the main reasons BB chose her as a contestant, it made her 'interesting,'  just as, for example, Pete's tourettes made him 'interesting.' Hence, for many, to now talk about Nadia, without remembering her and making reference to her as someone who has had gender reassignment surgery is v difficult. Also: we all have our own individual views as to what we see as 'masculine' and 'feminine' traits and how much we reject or accept 'stereotypical' gender behaviour, largely affected by our culture and our socialisation. I've seen numerous comments on here, relating to a number of hms which relate to these stereotypes, not just Nadia e.g. I don't think much of those guys in there, if a bloke had said that to me I'd expect my fella to punch him on the nose; she's really let herself go not wearing make-up or doing her hair etc. etc. etc. Additionally, gender identity is v important to just about everyone, so much so that those who feel that they are born into the the wrong gender body will experience such distress and go to such lengths to change this.... Nadia does often stand out as exhibiting what is viewed as 'stereotypical' masculine behaviour, i.e. aggression, which is presumably why some people find her hard to understand and come out with comments like she isn't a 'lady,' (incidentally that criticism was also levelled at Josie because she wasn't seen as stereotypically 'feminine')