On: You probably don’t need ReCAPTCHA

[mcv]

I'd much rather have a service where I can submit a comment to check if it's meaningful or likely spam, than to force my users to waste time and share data with Google that they don't want to.

If clearly spam, block it, if clearly okay, allow it. If unsure, leave it for a moderator. It might even train users to write better comments if badly written ones need to wait for moderation.

[vkou → mcv]

As if that's not a complete privacy nightmare. I'm sure either the NSA, or an ad-tech agency would love to get a firehose feed of this sort of data, while providing you with a YES-SPAM/NO-SPAM service.

Also, anyone who mentions <something the service wants to censor> can be, of course, blackholed as spam. ;)

[mcv → vkou]

As long as it's a public forum, I don't see the issue. It's going to be public anyway, and they could easily scrape it if they want to.

The submission itself should be done by the site, so the user remains anonymous.

[vkou → mcv]

There's a lot of information that can improve spam classification, that is not publicly queryable.

Any spam detection engine that asks for that information will outperform ones that don't.