Why not?

What would be a better reason? Or, do you think white people should feel free to use that word?

Because there was a time when white people felt free to use that word, and there are still pockets of white society where people feel free to use that word, and if you think those times or those people are good ones to emulate, I'd be quite interested to know why you think that.

A better reason would be, so as not to say hurtful things.

I think all people should feel free to use whatever words they want to use as long as they are speaking truth.

Why is "don't say hurtful things" better than "gain empathy and insight into the lives of a group of people who are generally very badly off, in very large part because our country allowed them to be enslaved for hundreds of years"?

Because it seems like "don't say hurtful things" covers a lot of stuff, but you miss out on the specific empathy this specific situation gives you by reflecting on why this one word should be taken off the table for white people.

Because the "gain empathy" argument is condescending and insulting.

What makes it condescending or insulting? I'm not seeing either one.

You're not seeing it because you are trapped in a class guilt, social justice seeking, identity politics bubble.

You don't know whether I'm trapped in anything, and I certainly feel no particular guilt at all about being a white dude; none at all.

Now, what's condescending or insulting?