In this one instance they might do that. In the area where I live where it was done, there was no space for the emergency vehicles to go in the other direction. Just because there are ways they could do it in this one case doesn't make it universal.
Also, are you able to provide the polling you referenced showing that highway blockades change minds? I was unable to find anything other than web and call-in polls, both of which overwhelmingly showed the exact opposite (but those are hardly scientific so I wouldn't trust them).
Also, I'm not the one downvoting you. I do not do that.
But come now, certainly you must recognize that that's not even close to causation. Just because it's done often doesn't even come close to meaning that there's any proof that it functions as you state.
If I carry a "rock of tiger repellent" and tell you that I've never been attacked by a tiger, therefore it must work, it's the same logic.
Countries that do not (or rarely) have highway blockades have more civil rights or had them earlier than the US did. They also have stronger protections and aren't helping bomb Gaza. Using the logic stated by you, that may actually mean that highway protests make things worse.
Again, just because it agrees with you politically, doesn't mean it's a good idea. There's no study or data indicating that it functions, and scads of loose polls and information saying it doesn't (which are only slightly better than no evidence at all). I'd encourage an actual study, but judging by every thread I've ever seen on the issue, the only people claiming to be even minutely swayed by these demonstrations were people already on the side of the protesters.