The neat thing is that if government provides identity, you don't have to use it for any system you build. But I'm curious how you would deal with spam and Sybils?
That’s not generally true, even if it may sound true in some specific location and time. Governments trying to mandate national authentication services is a very real thing.
As for your question: sadly, I don’t have a solution for either. I wish I would. I think ML-based approaches seem to show good promise for spam detection, though? I haven’t looked under the hood any recently, but purely anecdotally, almost every time I upgrade my mail system and antispam has something new ML-based, I’m getting a lot less junk. As for the sybils… I don’t think it’s an issue per se - an ability to have alter egos is not a clear negative. And then it must depends on the exact context. Government elections is one thing, online content popularity measurement is entirely different. Not sure it’s meaningful to envision any universal solutions - they tend to have too many side effects, and usually of undesirable nature.