I always find it funny how people get stuck on how impractical a bipedal war machine is, yet have no problem with some or all of the following:
Faster than light travel, Cold Fusion, sound it space, highly unstable ordinance, lasers with travel time, Gauss Rifles needing less energy than autocannons, Fusion reactors that explode in a fission reaction, etc.
Its all about suspension of disbelief. I remember listening to a discussion over how a spell should work in Dungeons and Dragons. One person was upset how "Fireball" did not create blast pressure or fill the space it contained. It totally broke the "realism" for this person. Magic needed to both follow the laws of physics, yet magic itself is pure fantasy.
Personally I see Mechs at some far-flung future plausible. Within the setting, planets are uncultivated and rough. Usually one major city, and a whole lot of wild terrain. There is lots of terrain that tread vehicles simply cannot traverse, and dust storms make 100% reliance on aircraft impossible. Someone figured out its easier to log timber from the side of a mountain with a bipedal Mech than it is to build a road for trucks to drive up. Then some years later someone put a couple guns on a Forestry Mech, and you have yourself a Battlemech.
I'm willing to ignore a lot a realism to have a walking tank step on a guy in battlearmor.
