And, "Both sides are bad" only provides cover to the side that is worse.
"Both sides are bad" is the only one that condemns and potentially fights back against both bad actors.
The "side A is worse" or "side B is worse" only condemns one, and bends over for the other.
GP is right. In equating a very bad thing and a moderately bad thing you only bring attention away from the very bad thing. This isn't theoretical - it's an empirical observation.