I, too, ask myself why I was willing to put up with so many unacceptable things. I've always had a hard time telling the difference between things I should take seriously and things I should not overreact about.
So far, it seems, that I have a good track record of flipping out over things that I should "let go", and not get so upset over...and then also brushing off things that I should take more seriously (like AH's antics).
Examining my "skewed radar" is of course taking me right back to my childhood. I think that it's possible that when you grow up in an environment that tells you what you are feeling is wrong all the time that you don't learn how to recognize your feelings in a proper way.
So, Cagefree, you ask: Why couldn't I be that protective of myself and let that guy just walk all over me so willingly?
Well, there's a lot to this...but one thought I have about why we allow people to do unacceptable things to us is that (speaking from my own experiences of course) when they happen we DO have a little voice (a feeling?) that tells us it is wrong...but we dismiss it because we do not trust our feelings/inner voice to guide us correctly.
I can't tell you how many times I ignored feelings because I thought they were being unreasonable and overreacting (well...hmmm, I was told my entire life by my parents that I overreact and "hysterical"....). I've learned to mistrust my inner compass.