It's not a matter of guilt. It is a practical reality of the ddos abuse on the net. It is massive and breaks network. It is all we can do to keep the net up at times. Serious.
Is the net up if we can't fully use it? UDP is an important part of the net. If we can't use it, then the net is not fully operational.
There are other ways to combat abuse than to filter out half the popular application protocols on the net. Eg start depeering ISPs who aren't swift in limiting/taking down their DoS spewing compromised customers.