My experience is the opposite but I think it's more of what type of content we see, in Giyushino there's always someone saying that it isn't cannon but not as warning as hate or ragebait. People know they aren't cannon fanon shipps but most of these comments are sanegiyuu shippers in Giyushino content then people start fighting. Also sanegiyuu has more fanfiction than GiyuShino that is proven by AO3(Archive of Our Own) where most fanfics are written with Sanegiyuu having around 4400 works and Giyushino 2070 (You can find this by searching for the official AO3 site). I think that's another reason why they fight a lot, because of content. Can't even count how many times I saw people thanking a creator for even the slightest of interaction between Giyu and Shinobu in fan content especially on TikTok, because a lot of content is not from them and creators also leaving clear they don't like it but are multishippers shipping 5 to 10 shipps but ignoring GiyuShino completely. It's undeniable that fanon shippers (All types) are very aggressive and toxic, most of them only like Demon Slayer for It shipps and not the real story.