okay, let's say wehr mirror on ango (which is a symmetrical map).
perfectly balanced, right? imho: wrong. south wehr is a whole lot easier to play than north.
similarly i'd prefer south langres, south semois, north sturz etc. etc. etc.
None of those maps are symmetrical in any way, other than the sectors on Ango and Semois. Even assuming what you said was true, which it isn't, but assuming it was, you'd still run into that problem without mirror matches: whoever gets to play the faction that's strongest on that map, in that position, would have a better chance of winning. That's a map imbalance issue, not a mirror match issue.
another thing i already mentioned, is that usually in mirror matchups the diversity of tactics that are available just isn't there (at least in most other RTS games). it basically is "do this build, or you risk getting your ass handed to you by a player that might not even be half as good as you are".
That's a crazy assertion to make considering the alpha has only been out for but a few days. Even so, that would be an issue with intra-faction balance, and to my knowledge, most people in favour of mirror matches have stated quite clearly that if the mirror match balance just isn't working out for Relic, then they shouldn't be in the game. Nobody wants that kind of imbalance for any of the factions, mirror or not. But that's not an issue that's solely related to mirror matches, and it's certainly not a reasonable argument against them.
also: if you think there's been no points made as to why mirror matchups should not be in automatch, then you haven't read this thread at all, which is a shame for coh2 :-P
Please quote every single reasonable, well thought-out and supported argument against mirror matches in this thread.