Slavery isn't inherently racial and it is generally an economic (and often cultural) thing. But the Transatlantic slave trade and American slavery specifically were most definitely racial.
None of that has anything to do with the comparison between Roman slavery and American slavery and why the latter is obviously more relevant and talked about a lot more in America. Completely irrelevant.
One would have to be blind or stupid to deny that it had a huge impact on the development of modern American society.
It's also important to note that black people didn't exactly receive equal treatment as soon as slavery ended.
The Civil Rights era also didn't solve all the issues for the black community.
To get back to the original point about black pride and black history, it's about a lot more than slavery.
Limiting it to that and saying they need to get over something that happened over 100 years ago demonstrates ignorance of what the thing you're arguing against is actually about.
Also, I don't think 150 years is as long a time as you seem to think it is.
John Tyler was president in the 1840s and he has living grandchildren. It's not ancient history.
And this is relevant to the topic ... how exactly?