As someone who was semi-involved in the fandom at the time of this shitstorm ( basically all of my favorite characters were dead, I just followed along out of obligation at that point ) I would like to respectfully disagree with part of this post -- yes, there was a subset of fans who disliked TouKen because it wasn't HideKane, and yes, the backlash against Ishida was absolutely disgusting and unjustified.

However, I do recall a lot of the controversy centered around Touka herself -- not that she was a woman, but because she had a tendency to be verbally and physically abusive towards Kaneki. You could argue this was simply playing off the whole anime slapstick trope, but considering Kaneki was canonically an abuse survivor who was hurt in a similar manner by his own family ( and it was played completely straight, we see him being beaten as a child ) it really left a bad taste in people's mouths. A lot of fans didn't want to see Kaneki end up with someone who resembled his abusers. You could argue the intention was never to portray Touka as abusive, but again, when Kaneki's upbringing was treated completely seriously, it's hard to stomach seeing someone else smacking him around.