Trustable or legitimate for what purpose? As a reliable information source? As an entertainment source? As just one among many media sources? To bet your life on? ?
As to information, probably less than 10% of the total volume out there. For the rest - more than for information but who really knows?
For a start, approximately 60% of everything on the internet is pornography. Do we trust porn sites? ... Personally, when it comes to monetary transactions, I think I'd trust far less than 20% of the internet, so that's how I've answered the poll.
There are many ways to verify what you find on the net. By double checking what you find or by asking others as to the products reliability is but only a few ways to verify what you learn on the net. Those that use this net to just make life miserable for those naive enough are they themselves going to lose out in the long run. They will eventually be found out and people will stop using their sites as time goes by. True, there's always new sites starting up that will also take advantages of unaware people and that can't ever be completely stopped but only slowed by education and word of mouth.