What's stopping you from allowing zip files? Are they published on a website or sent by e-mail? If someone downloads a file with the extension "zip" and that it actually has an "exe" extension, is this a problem? If you are concerned about malware, you can still run a script that automatically checks for the presence of malware in the downloaded content before releasing it.
Depending on your question, it appears that you are concerned that incorrect content is being downloaded. So you need to think more about how the community can control content and add your own controls (malware correctors, clamav) to protect it, and then block people who abuse it.