I think you should understand the terms as "toxic masculinity" as opposed to "positive masculinity". It's not saying masculinity is toxic. Or if you want, as opposed to "true masculinity" - reframing masculinity as a positive thing when expressed correctly.
Toxic masculinity doesn’t mean men are poisonous.
It means men are being poisoned.
Why do undesirable or desirable behaviours need a sex/gender label at all? Asshole behaviour isn't gender-specific. Maybe people should just focus on criticizing specific undesirable behaviours, and praising specific desirable behaviours.
In practice, the term is never used this way. It's used as a cudgel.