Is it normal that i can't refuse blow job?

Perhaps luckily, I'm not some hot stud that girls just inexplicably want to blow, but in my life, anytime a girl has offered to go down on me, I can't seem to say no, even against my better judgement.

I have managed it *once,* a woman I knew who was a prostitute offered to go down on me for free one time because "once you're in my mouth once, you'll be glad to pay to have it again." Actually, I found the whole thing disgusting and politely declined.

But other than that one situation, I've never been able to refuse it. Ex-girlfriends who think we'll get back together, offering it as a favor in trade for a favor (never for money, however), dangerous places we could get caught, whatever... common sense tells me I shouldn't, but I always do.

Is this normal? Does the female mouth have this much power over most (hetero) guys? Or am I weird, stupid, sex-addicted, etc? I'm curious to see how other guys reply to this.