As for why neutrality is a good thing, well, the simple argument is that I've paid $X/mo. for a particular service. That service is an Internet connection at a certain speed and up to a certain amount of data transferred. Not "an Internet connection unless I use Skype or watch lots of Youtube videos, in which case it gets throttled -- sorry, 'quality-ensured' -- down to a trickle".
And that's as it should be, because that's what fosters innovation: if new and interesting uses for an Internet connection have to contend with throttling and degradation imposed by companies which are already being paid to provide the bandwidth, well, it seems to me that there won't be nearly so much innovation.
Is that reasonable grounds for regulation? History seems to think so; we've been enforcing common-carrier status on various related fields for quite a while now, and it doesn't seem to have caused floods of lawsuits or hampered innovation or infrastructure as the free-market argument says it should. And it should of course be noted that the cozy relationship AT&T had with the government (which regulated the hell out of it for many years) made it profitable enough to sink huge amounts of money into R&D, giving us Bell Labs, etc., further putting the lie to the free-market argument.
And, of course, that's without getting into things like subsidies provided to telecommunications companies to get them to build out infrastructure (since one consistent claim is that there's just not enough bandwidth to go around, this is particularly relevant) -- so far as I can tell, they've yet to hold up their end of that bargain, but I think the people who've had to foot the bill for them have a right to expect them to.