What if the reason the Beta trolls are so fucked up (Kanaya's weird fondness for fashion, Equius' abnormal strongness, Gamze's Gamzee-ness, etc) was a result of Karkat giving everyone cancer while doing the ectobiological thingy?

I doubt it.  Their dancestors share those specific traits.  If you haven’t noticed, post-scratch troll society was kinda fucked up. Aradia was a ghost, Terezi was blind, Tavros couldn’t walk, Vriska lost an arm and an eye, Sollux went blind. Those weren’t caused by ectobiology. The trolls were just in-general fucked uo

~Mod T