I seriously hate when people try to have intelligent discussions about "mechs" as viable tools of warfare. Yes, you dolts have the basic arguments down: They are science fiction machinations, based on technology that is not entirely developed at this point in time. The rest of your arguements are not only moot but in the typical conservative fashion, pointless, irrelevant, misguided, and asinine.
"The M1 Abrahms 70 ton AFV has its mass distributed evenly amongst its tracks, that's why such a heavy vehicle is able to be successful."
Mecha are humanoid. Every last detail of mecha in a decent "mecha" universe (i.e Battletech) is thoroughly explained and dignified. Human beings are able to walk and not destroy things under them that are structurally stable, without falling over or imploding. Sorry, there's no counter argument for that. Increasing the variables on both sides does not change the math, it still comes out as viable.
Combat nowadays is urban? Does that matter at all? No, it really doesn't. If you are too damn stupid to realize, the combat in Battletech rarely takes place in urban environments and when it does it's dangerous and disasterous in the most realistic of ways. Additionally, if you were to presume combat even occurs in an urban environment, bringing with it all the intricacies of a city (sewers, plumbing, electrical wires, roadbed, bridge support, foundations) you have to use the common sense that the majority of 'mechs in the situation are going to be light, in the 20 - 40 ton range. Twenty to forty tons distributed over two humanoid legs will probably destroy a roadbed, yes, it's irrelevant. Building a city requires ground. The ground didn't disappear, it's still there. Trust me, I've seen it.
And just how is height a disadvantage? How retarded of a suggestion is that? This isn't Bag End, it's reality, it's outside. Being 40 feet tall isn't going to do anything but make it easier to see and kill everyone.