I just googled youtube downloader and guess what..... dozens of sites offer download software or ways of downloading from other similar streaming sites. I was dizzy scanning through the list. Now I am no legal expert but if folk are serious about protecting their original material then it would be relatively simple to sue these companies. What they offer is clearly illegal. At the very least they are inciting people to break the law and on that basis could and should be shut down.
I say go for these big boys FIRST before picking on little old ladies or college kids.
Whilst I know that Youtube downloading is wrong I bet the vast majority of folk think it must be Ok if companies openly offer this service. They see little difference between watching something freely available to anyone and downloading a copy for their own personal use.