> you think we should let criminals access the internet anonymously?
Of course we should, because that is unavoidable. Making anonymity harder will make it so that only criminals have anonymity, because they are the ones who can justify extraordinary measures and are willing to break laws in order to get it. All laws against anonymity do is harm honest people who need it for anonymous speech and privacy.
And somehow all of your premises are wrong, even though only one has to be for your argument to fail:
> Internet is not really a public resource, it's rather a gigantic alliance of p2p connections, mostly organized by private entities who can make whatever contracts they want.
This is like saying transportation isn't a public resource because buses and taxis and airplanes are provided by lots of different people under privately negotiated terms. You don't have to show ID to ride in a taxi, nor should you.
> On this alliance, if one actor wreaks havoc (spam, DOS, scam, piracy), the victim can only turn back to the node which transmitted the connection
Victims of scams can follow the money or flow of goods. Spam and denial of service can be algorithmically identified and rate limited. Undetectable piracy is not a problem your proposal would solve; see also direct download sites, foreign VPN services, I2P, sneakernet, LAN parties, etc.
It is also possible for endpoints to choose to require that the opposite endpoint authenticate cryptographically before accepting any other data from it, which will always be significantly more reliable then relying on every carrier and endpoint on the internet to remain uncompromised in its ability to assert the origin of traffic it forwards.
> It's up to this node to keep logs and forward the pursuit upstream to the attacker
This isn't a premise at all, it's just an unsupportable conculsory normative assertion.
> It's the only way it can decently work, because we may lack proofs or the chain of responsibility to attack the upstream node directly
So block it until the attack stops then. Or require users to register using some collateral or proof of work.
> Legal problems will happen if we treat the Internet as a public resource, where politics have a say, where access is not authenticated, and where no-one bears responsibility for crimes.
Just because an IP address doesn't map to a person doesn't mean "no-one bears responsibility for crimes." It just means investigations are more expensive. Which is good, because it means serious crimes can still be prosecuted but mass surveillance and petty crusades are impeded.