It's very frustrating that behind every "you should be eternally grateful for every child no matter what" warm fuzzy message is an implicit "and if you ever express regret for having a kid who wound up non-verbal and violent and destroyed your marriage and your relationship with your other kids you're a horrible person".

Not referring to your cousin specifically but my mom's life's work is with severely autistic children (the "can't talk and hits people" sort, not "I'm a bit awkward and love math and doing anything to help autistic kids is abject cruelty!" sort), and the experience for parents mostly seems to be abject misery.