Why is it not cool to say that all lives matter? Aren't black lives part of that?

Because it is intentionally addressing only the linguistic logic of the campaign slogan.

It is deliberately ignoring the historical reality (i.e., the overwhelming evidence on record) that society has systematically treated Black and Coloured Americans as though their lives are less valuable and less important than those of whites. This post was edited by inky at June 11, 2020 10:23 PM MDT

i think its cool to say that