lol, I thought this post might cause a bit of a turmoil . . .
Without seeming to apologize let me clarify a bit.
Long term relationship to me usually means something like a 6 week relationship with a 2 year break-up. Most people seem to stay WAY past the point of unhappiness with unsuitable people.
KilarneyRose has a good point. Interestingly enough almost every woman I have met seems to be a pessimist when it comes to themselves, whereas almost every guy I have ever met seems to think he is a gift to womankind (an attitude that works with him). Seriously, I have seen the most appearnace and personality challenged guys look in the mirror before going and out and be like, "I'm going to get me some tonight!"
I think, and this case I know several guys that do this, we are not precisely judging the woman as an individual per se, but rather judging a situation. If a girl is willing to spend huge amounts of time in an unhappy situation, and with someone that doesn't treat them well, they don't necessarily seem like the greatest candidate for emotional investment, she might not have the reference points to actually deal, appreciate, or reciprocate.
Also, guys tend to be super competitive among other guys, and it seems that we might be placing ourselves on the same level as another guy by dating the same girl he dated . . . Which is not fair, but we don't live in a vacuum and many of our judgments are socially affected.
This actually places like aside and applies more to first meeting and sizing the person up. Obviously when we actually start really liking someone we will make all kinds of allowances.
Oh and what worriedsenior said is very true, I can kind of dig someone for any number of reasons . . . but I have yet to fail to see when killer eyes hides severe personality problems, or stay in such a situation for a long time.