Men struggle with gender expectations (some).
This is much the same as for Sun in Libra, but perhaps with more friction over it. One of the most important considerations in interpreting a natal chart is to look for places where the "outside voices" (the world's expectations) agree or disagree with (support or resist) what one really is. One of the most pronounced areas of this is gender roles. As a simple rule of thumb, if something in the chart shows strong tendency to cultural gender stereotypes
and these match one's actual gender, the primary experience is that the world supports, encourages, and accepts who you are; but if if it is the opposite gender, the world is more likely resist, discourage, fight with, and put down who you are.
This basic feeling difference of the world resisting vs. supporting who one fundamentally is can be a far stronger factor in one's life than the details of the particular factor itself. A consequence is that (as a generalization) women (girls) with Sun or Mars in Libra tend to thrive and men (boys) with Sun or Mars in Libra tend to feel minimized and sidelined, most typically reacting with extreme overcompensation.
This, of course, is stronger and places and times when gender roles are most rigid. I imagine we will find that it's less true for children born today than children born even 20 years ago, and especially 40, 50, 60 or more years ago. In the '70s, '80s, and '90s you could pretty reliably say of a Libra man that unless he was openly fem-gay or a successful competitive artist, he was likely to act minimized, withdrawn, over-compensating, likely a bully, etc. There simply weren't cultural outlets for a man to act in overtly feminine ways. (One can say much the same about Aries, where most of the women haven't done so well historically unless they were born into a place of command or found a covert means of control and domination, but the men are allowed to thrive just fine.)
I've often thought that Bradley's insistence that Libra is "the black sheep of the zodiac" - something I find obvious enough with the Sun but much more obvious with Mars, which in Libra seems much of a "social outlier" - is because most figures studied were men where this characteristic is historically more obvious.
Ego distinction prevails over ego-submersion (but wants marriage).
This was my language to try to balance two traits that seem "either-or" and at odds with each other, but which seem (based on observation) to co-exist comfortably enough in Mars in Libra people. (I observe this especially in Libra Mars women but don't doubt that it's equally present in the men: it's just more like the cultural norm expected of men, so less visible.)
The first trait is that they really do want marriage. We have one important statistical study showing that Sun in Libra men are the most likely to marry of any sign type, and this behavior and these choices seem matched by Mars in Libra. They want to marry, they'll tell you they want to marry, they act like they want to marry, and usually they marry.
The second trait is that - unlike most other sign types when they are way
into getting married - Mars in Libra people maintain an almost aloof independence. They don't slide toward merging
with another. It's not as simple as wanting both people to retain individual choices and be supported in their careers and other life priorities, it's like (or, from the outside, looks like) their actions are constantly affirming their ego-distinction. When I talk to those I know best, some have seem puzzled at the observation: They think they're partnering
as much as anyone else does. But their words, body-language, etc. are routinely more like that of single people than like closely partnered people.
Struggling with these facts for a while, I finally saw a path to explaining them by merely acknowledging the co-existence of the seeming
contradiction: As a group, they definitely want to marry AND YET maintaining ego-distinction
is more important to them than ego-submersion
(submerging their egos into the duo).