The idea behind black lives matter is that what we're really saying is black lives matter too. Meaning in addition to white lives. Which came about because of a bias in the media that portrayed white criminals as having complex backgrounds and trying to humanize them, but never doing the same thing for black criminals.

For black criminals the media usually played it like they were inherently criminal. Nobody really loved them and the police were just doing their jobs cleaning more trash off the streets.

BLM is therefore as much an issue of empathy as it is anything else.

Whataboutism in the sense of "men too" is therefore the exact same thing that BLM is founded on. People don't care about men and men's issues so we're trying to spread the word and develope a similar culture of empathy for men. We say "men too" not because we want to take anything away from women, but because we want men to be given the same consideration that we already afford to women.

Unlike the issue of race, I don't think it's clear that men or women have things uniquely better or worse compared to one another. The biggest difference is the fact that we care much more about women than we do men, including even when men have things worse (for example when it comes to homelessness or incarceration). Which is itself an example of sexism against men and actually mirrors the very foundation of the BLM philosophy on race. It's seen as a tragedy when a woman is homeless or is locked up or shot by the police but it's just normal and accepted when the same thing happens to a man.

Which is why we say "men too".

Mens issues matter and men's lives matter.

Anyone who says otherwise is missing the point and doesn't understand what BLM is supposed to mean.