Also calling people 'autistic' and later calling people with autism 'it' as in 'try to injure itself' is a really shitty way to talk about human beings. Check yourself.
mamcx is not a native English speaker and was perhaps trying to use "it" as a gender-inspecific pronoun rather than intentionally portraying people on the autistic spectrum as "objects" or "inhuman."
I think most people will tend to use a plural (they, them) in this kind of situation. People who are pickier about grammar will probably say "he or she" or "him or her."
People-first: http://www.asha.org/publications/journals/submissions/person... and https://en.wikipedia.org/wiki/People-first_language
Identity-first: http://www.xojane.com/issues/i-am-not-a-person-with-a-disabi... and http://cheshirekit.wordpress.com/2014/01/23/the-social-model...