Don't feel bad, its not like you're endorsing everything about Barkley or are expected to know everything about him. His reputation amongst basketball fans is mostly "lovable goofball who says mostly stupid things that get made fun of, and every now and then having a good take", so its pretty in line that this is his one good take amongst many bad/stupid ones. He also always said he never wants to be a role model and doesn't believe he has much influence over things so he can make the jokes he does about homeless people or overweight people, so its unlikely he'll ever be known as someone without some shitty opinions. Its still better that he is saying this rather than saying nothing or saying something shit about gay/transgender people.