A couple things there, @Healandlove :
1. IMHO anything that is (or ought to be) a universal human trait can't be classified as a masculine trait, since the very act of sub-categorizing a segment of humanity as masculine implies that there are traits that distinguish them from the remainder. Thus, to me, it doesn't make sense to say that masculinity ought to mean: "sharing emotions, being vulnerable, having emotional regulation..." if you expect these to also be traits embodied in femininity and any other non-masculine identity. Your describing the idealized human, not the idealized man, which would be an idealized human refined down further with additional criteria.
2. I suspect that pressure to share emotions and be vulnerable may be part of the problem; particularly in situations where doing so would be unproductive. It's hard to imagine, in fact, how vulnerability could be a good thing. It'd be great to be as strong as Achilles; it would be even better to be that strong, but without the notable vulnerability of his weak heel.
And the pressure to share emotions - particularly in situations where emotions don't really exist to any noteworthy degree - may be part of the problem; as if the modern world might be encouraging young men to take on the role of emotional trainwrecks - perhaps not on a permanent basis, but certainly more frequently then has been the custom in previous generations.
I don't know. I just get the impression that there's a burning desire within a large segment of the community for the "classic male"; the John McClane archetype who can get shot 30 times and still limp along to take out the remainder of the bad guys, without whining or complaint, as long as there is life still in him. That's an exaggeration, obviously, but I think there's an enduring natural attraction for that sort of stoic just-get-on-with-the-job-at-hand-and-don't-make-any-needless-fuss type of character, and the people who yearn to live according to that conduct are being told that they aren't aloud to do so, and that the society they yearn to be a part of - made up of such people - will not be tollerated.