It's mostly been said - yes, we do need unions. And, if you don't like what your union's doing, remember that it is your union and get involved.
(That said, there are some crap unions, at least in the UK. The NUJ takes the biscuit for being the most inept, politically flaky and absurd union around - but at least it tries to look after the interests of low-paid hacks on provincial papers, who make up the bulk of its membership)