Ehhh... first of all, using autistic in a derogatory sense is pretty ableist and disgusting. Secondly, furries aren't theriand, dumbass, and not even therians want to become another species, they just feel strongly identified w/ it. Like otherkins, but with real animals instead of mythological creatures.
And like, could you substantiate how dressing as an animal proves you're mentally sick? when I was a child I wore a puss in boots costume almost every day, and that wasn't a symptom of any mental illness.
Also, don't kink shame, some people just get horny from getting put in a collar.