It's actually not that, surprisingly. It's that he doesn't write women WELL. His women are very much "men with tits," and often feel shoehorned in, rather than actually organic and unique. His older books were much better about this, but his newer work definitely feels more "forced." He's even outright said that he has a "quota" for how many women and non-white characters he has, which on the surface doesn't seem bad, but in reality you've just put those demographics on pedestals in your works, which I feel is not the point of this setting.

Furthermore, he pushes for female characters in some of the VERY few areas where they cannot be, like Custodes and Space Marines (he lobbied very, very hard for there to be female Custodes, and only relented when higher ups basically told him "absolutely not,") Those are the ONLY two places I think that we should not have female characters for very explicit lore reasons - literally everywhere else they are welcome. I don't like when people try to completely re-write one of the very few hard rules of the setting just so they can write their own unique story, which is what ADB tries to do.

His twitter is also a bit...rough. Some of the things he's said are just a little much, and it honestly just reeks of "wokeness" and White Saviorism (kinda also shown when his OC Donut Steel chapter The Emperors Spears swoop in and save the "not-African" Celestial Lions - by itself not a big thing, but combined with everything else it takes on a new meaning), which does not sit well with me.

As somebody for whom activism and resource development for women and non-whites, and empowering them to help themselves in the professional world, is literally part of my job, ADB's brand of "wokeness" is almost as harmful as it is helpful, because it's done for all the wrong reasons and doesn't actually HELP.

TL;DR I 100% agree with his ideas, but his implementation of them is bad, inauthentic, and doubt his motivations are genuine.