Yes there are. but using your source address means that you are confined by the upload bandwidth of your hosts, instead of some mis configured DNS server with

Yes there are. but using your source address means that you are confined by the upload bandwidth of your hosts, instead of some mis configured DNS server with a 1000Mbps up in a datacenter. You'd just have to work a lot harder to get the bandwidth. to add to that, You'll defiantly get some mis configured servers with 1000Mbps uploads. And those will be really easy to pick out of the lineup. And then you'd probably be able to call the DC and say that they should block that IP at their boarder and they would probably also comply because there's a good chance that customer that was doing 110Mbps and won't want to pay for 1000. As it is now, because the source is spoofed, you can't really take the source offline, only take the destination down to keep the other hosts in close proximity running. With a TCP connection you can pick the source and drop the handshake, basically never start the connection. Some of the windowing can be used to make a tcp connection less of an issue as well.