This is an important thing to understand on Mastodon: you don't see all the replies to a post. 

It's possible for evil people to propagate terrible hatred that only shows up for the person being attacked, but isn't visible to you.

See explanation from nostr:npub14ukaj9jxt92unn28r7z42n475c7u6typ2cu8wyur4eqrk67tyz9sxs2erc here: https://hachyderm.io/@mekkaokereke/111012743709881062

When Black users tell you there's racism, it doesn't matter that you didn't see it happen.