You are racist. You are sexist. You are homophobic.
Now stop. Analyze your response to my words. Is your heart racing? Do you feel tense, ready to fight? Are you already in my comment section, blasting off a response about how you have plenty of black/gay/disabled/women friends and of course you don’t stereotype? Are you ready to find holes in my argument and punch right through them?
If you want to be a true ally, you need to realize that this type of response is happening. When someone questions you, or calls you biased, you immediately have physical and mental urges to defend yourself, to fight and stick up for yourself. This immediate defensive response is not conducive to having a well-reasoned discussion about whether you actually have a bias. You are likely to shout at your ally, find excuses, and otherwise alienate them. If you truly care about your allies, you need to learn how to suppress that response.