I think it's how you look at a soul mate. If you look at a soulmate like a picture that you stare at and always see the same thing and you don't expect it to change (I mean it's a picture) Then yes, you will always be disappointed by the concept of soulmate.
However, if you see the soulmate as a person who is human, who is ever changing, but you are connected in such a way that you accept those changes. then yes the soulmate is alive and well.
I'm convinced my W is my soulmate, no question. But just because I get mad at her or frustrated at times doesn't make her any less so.
I think not believing in a soulmate is a convenient way to let your self out of relationship in the need arises. I mean hey, they are just another person right? Any warm female could fill that role with the right "training."
Patience is bitter, but its fruit is sweet. --Jean Jacques Rousseau.