SLT or DSLR?

Can anyone explain to me (and I'm not starting an argument here, I truly want to know before I purchase) why many DSLR photographers won't consider the Sony SLT cameras for serious photography? I already know how the technology is different (at least in a broad sense), but does it actually affect the results? I have almost purchased the Sony a57 several times but keep holding back until I've explored this.

Thanks so much.