Thanks for the valuable comment. I will try to name solutions for each of the concerns you listed. Tell me what you think of those:
1. Spam: Humanity verification + A Negative Points System*.
2. False Reports: Negative Points System.
3. Reporting Disagreements: Negative Points System.
4. Ignored Reports: Regular Reminders. Prioritizing content that multiple people reported.
5. Acceptable Content: The community owners decide standards. Not this system. The owners can merely use this as a tool for reports to come in.
---
Negative Points System: Everyone starts with a X number of points. Each report decreases X. If a report is constructive, they get back decreased points, plus earn some. If the report is well intended, but doesn't justify a report, they get back points, but earns none. If the report is malicious, they lose their points, and some more. The pluses and minuses can indicate a user's behavior, and the owners can remove that user's right to report.