I'm not talking about being mild-mannered. I don't expect or want someone to speak calmly about racism if they have been subjected to it their entire life. It's not reasonable to expect that, and I would rather hear what you really think and feel than have it sugar-coated to spare my feelings. I can take it, or I wouldn't read essays like this.
I'm talking about getting your facts straight. If someone refutes a false premise in an argument, they often convince themselves they've proven the conclusion is false. Your essay has lots of strong arguments, but one weak argument can draw attention away from the strong ones. So my suggestion is make sure that you can back up everything you say, and when in doubt, leave an argument out.
There's a big assumption in our culture that being reasonable and being calm are the same thing. Our legal system, for example, will overturn a verdict if the judge's final statement is too angry. But this is a mistake. There are a few writers who can combine impeccable reasoning with righteous anger, and it's often the only appropriate strategy. Ta Nahesi Coates is my favorite example. He never hides his justifiable anger, and he makes you feel the anger with him. But his arguments and research are impeccable.
Sorry if this sounds too pedantic. I've taught critical thinking in college for 20 years and sometimes the inner teacher gets unleased. Hope you found this helpful and supportive.