I tend to visit more culturally diverse - often developing - countries but maybe I need to look deeper into Australia!
I think it'd be worth looking into, at least. Australia's seemed fairly diverse to me so far. Melbourne, for example, is quite an international city.. a great Chinatown, Greek town (the largest Greek population in the world outside of Greece itself), etc. Something like half the nation is a first or second generation immigrant. :)
Disability discrimination really does surprise me, but maybe it shouldn't. Maybe it exists here in the US also and I am not aware of it.
It's huge in the U.S. That's why we have the ADA (Americans with Disabilities Act), because of the massive and historical discrimination against people with disabilities. And there are violations of it all the time. At least we have it as a tool to help protect them (of course they still have to sue to get it enforced).
Nowhere's perfect. I just think it'd be a shame to disregard a whole continent for the ugly behavior of a few.
I'd be arguing just as hard to someone saying it's not worth visiting the US because of the racism we experience (via explicit things like cop shootings and racially biased justice system, and via casual racism as is found in the South). The US is a huge, diverse place, with many wonderful people (and many not so wonderful). I can't guarantee you won't experience some form of ugliness, but I've experienced some of that in various places around the world, and I wouldn't hold it against a whole country, personally, or let it stop me from seeing all the amazing, beautiful, and wonderful things they have to offer.
Again, YMMV, and I totally respect your choice to travel--or not--as you wish. You're absolutely right to be concerned about it, and consider it. I'm just giving you a little something to think about, perhaps, about why it may be worth it, anyways. :)