Banning someone based on the fact that they used the same (best known) proxy as a spammer is nonsense people use proxies to access this site for completely legitimate reasons. And Patricia is wrong to say all you can know about someone is their ISP if you know their ip address.
Quick examples ryanair employees were slagging off people criticising ryanair or linking to special offers the ip was traced to ryanair who admitted it was them. Various people have been found to have edited their own wikipedia entries by tracing their ip.
Also many employers block access to adult sites one way around this is to use a proxy. All you have shown is that you are completely clueless if you think using a proxy means bad intention.
If you know someones ip it is easy to find put who they are or at least who pays the bill this is not a "normal" forum so it is completely legitimate for users to hide their real ip for their own security I have done it myself when accessing from work.
Its the Crips and the Bloods all over again