Sure, and I'm sure people were mad when it was first used as well.
Say someone is trying to get to the hospital because they have a child having a severe asthma attack in their backseat. They just got on the interstate, panicking because their child is wheezing, and all of a sudden, they have to come to a complete stop. No cars are moving whatsoever. The child's wheezing gets worse, and the parent gets even more freaked out. Finally, after what feels like an eternity, they get to move again. Why the sudden stop? A bad wreck perhaps? Nope, some protestors holding signs. The parent doesn't care what the signs say, or what the protestors stand for, they are just pissed that they got stopped from getting to the hospital to help their kid out.
Perhaps that's an extreme example, I'm just trying to get my point across that blocking traffic, I think, does more harm than good for trying to get people to support your cause.