The real problem is the flip-side of something that the OP mentioned as an advantage: ASP.NET coders tend to be cheaper, less experienced, and hence less likely to know about some critical detail that'll boost adoption, whether it's usability or latency or security. As someone relatively inexperienced himself, the OP can't know what those things are, but it's highly likely that one of them will bite him.
In other words, it's correlation, not causation. ASP.NET won't make your site suck. However, ASP.NET biases your talent pool towards developers who suck, and that will make your site suck.