Negative sides of using proxy?

The only actual downside I can think of to a proxy is that you don't know many times who's running that proxy. Sometimes you have University proxies available that should be somewhat reliable, but, many of the proxies out there that you get out of lists and whatnot are some individual's proxy that may have been setup to trap you. People don't realize than when they are using a proxy they are using some machine that's been purposely setup for people to jump through unlike the N routers out there that constitute the inner-workings of the Internet. Whoever setup this machine can be looking at all the unencrypted traffic that goes through it and with the right knowledge it can just place itself in the middle in such a way that even while you think you're sending encrypted traffic you're outright handing out to someone your bank account login details. So, if there's a negative side to blindly using proxies, that's the one. The speed matter, well, that's all due to being a crappy proxy because a proxy is much like any other device that you have to hop through on the Internet... a proxy with a good bandwidth availability and you'll notice no impact on your speed. As to the being banned from the money making programs neither, that's not really a negative side because you're the one trying to scam a company... unfortunately, someone else already thought of that before you and because of everyone trying to use the same proxy they get to know what's going on.