[ozozozd]

Why?

If there is technology and established protocols to prevent spoofing, but some ISPs refuse to follow these protocols, why should it be your burden to prove it wasn’t you?

Is it reasonable to allow people to get credit cards with your SSN, when it’s physically possible to confirm their identity when they present your SSN, but the bank is too lazy to do it, and we put it on you to show up and cancel the credit cards? And of course present 3rd party attestation that it wasn’t you who did this. Maybe even bring an alibi?

I hope I misunderstood your comment.

[tmcdos]

Some ISPs (often those of the "last-mile") allow outgoing packets whose source IP does not belong to their subnet. They have no rules in IPtables preventing packets that do not belong to the given subnet assigned to end customers. This is how spoofed packets enter Internet most of the time. The ISPs on upper tiers can not use such filters (even if they want to) because their networks are not strictly hierarchical like the networks of the "last-mile" ISPs and such filters will simply break the connectivity. The only way to significantly reduce spoofed packets is if all "last-mile" ISPs implement proper filtration.