Because this is such a vast issue, I'll only touch on a few points.
Men's lib sees men's problems stemming from the Patriarchy, male traditional roles, and individual men themselves--basically men are the cause of their own woes, both collectively and individually.
This attitude allows them to snuggle, welcomed, in the bosom of feminism. Criticism of feminism is taboo, as is criticism of trends of negative behavior in women in general in society, or the behavior of individual women.
The problem with acting within these restrictions of thought is that if your premises are wrong and incomplete then your conclusions will be wrong and incomplete too. MRAs want to factor feminism and the attitudes and behavior of women into the equation.
If feminism is causing or exacerbating some of men's problems, then men's lib will be blind to this. If the common behaviors and expectations of many women push men into restrictive gender roles, then that will be screened out by men's libbers' blinkers.
A couple examples of the latter here:
The majority of women "marry up," to men of higher education, status and wealth. Then when it comes to having children "it just makes sense" that the woman has the choice of staying home as a full-time mother, coming back to working part-time, or full-time (with a nanny or daycare). The man in this situation faces increased financial pressure to be a breadwinner and by agreeing to this role loses all of his potential options.
As here, there's this idea that men need to learn to be emotional and sensitive, as if by doing so they will be freed form depression, suicide, and so on--but there is a huge factor missed out here.
Girls and women are typically more free to be emotional, to break down, to seek emotional support because by doing so help will come. There is no point getting boys and men to be all soft and vulnerable when there is no compassion, support, and help there for them. It's just leading them to breaking point.
I can't see men's lib being helpful when it willfully only takes part of the reality of the situation into account, and accepts misrepresentations of reality as the truth (e.g. Patriarchy). Garbage in, garbage out.