I used to CPU mine...while we all know someday we're gonna need super high power computers to run a huge network, we simply don't need that much processing power right now.  That said, the more powerful hashing devices we create, the more we need them to protect our network.  If someone decided to make an ASIC back when I was mining with my laptop, they'd have owned the  then rather puny network (and might not have cared if they trashed it...bitcoins weren't worth anything back then).