I totally understand why you are doing what you are doing but still it's a huge issue. Watching CSAM is also punishable so you better won't check your servers for CSAM for the purpose of reporting it without legal advice neither. I think, CSAM or other illegal material is a high risk thing for nostr as you can all too easily end up downloading it and by that commit a felony. So if all the hosters filter using centralized filtering services, it's all centralized and if they don't filter, the end users all become culpable of crimes they never intended to commit.