.... And at least in New York, it's almost impossible to go below the speed limit and not obstruct traffic. And why should traffic ahead of you be allowed to force you to drive below the speed limit? That's what you do when you drive below the limit: you force everyone to drive slower than they want to!
On the other hand, though, if you follow that argument to its conclusion, then the signs that a number of states and provinces use posting minimum speed limits (e.g., "Speed Limit 70/Minimum 40" or Quebec's oft-used "Maximum 100/60 Minimum") would be irrelevant or inaccurate because people "shouldn't be allowed" to go slower than the posted maximum.
I'm not arguing that being stuck behind someone going below the speed limit isn't damn annoying in many cases, especially on a rural two-lane road with no passing zones for miles at a time. I just don't agree that the mere fact that the sign says the speed limit is 70 mph means you automatically have a right to go 70 mph. The signs on the Garden State Parkway that say "Speed Limit 65/Conditions Permitting" underscore the principle pretty well—most people would agree that in bad weather you might have an obligation to slow down, for example, but "conditions" can also include things like sun glare or traffic.
Or, put differently, when I was learning to drive my father said, "Sometimes you get stuck in a situation where the speed limit is 65 but the traffic in the right lane is doing 60 due to a slow truck and the traffic in the left lane is doing 75. In that case you either slow down and get in the right lane or you speed up and get in the left lane, but you do not tailgate just because you think the people in the right lane are 'too slow' and you do not block the left lane just because you think those people are 'too fast.' You adjust your speed to one lane or the other."
(I feel VERY strongly about lane discipline and keeping out of the passing lane except to pass, to the point where it sometimes drives my wife crazy because I'm always moving back to the right. But I HATE it when someone is blocking the left lane unless there's a compelling reason for it like debris in the other lane. BTW, I say "keeping out of the passing lane" to account for countries where you drive on the left and the far right lane is the passing lane.)