So even if the protest were against Haredi draft evasion, you would say this is an illegitimate protest tactic?

Not legitimate

If so, then the government can oppress the people without limit, and the people have almost no ability to do anything at all—
just stand nicely on the sidewalk and politely ask the authorities to mend their ways…

Democracy has a price

That is exactly what I meant when I spoke about dose. The dose is made up of two components: the intensity of the distress (the reason for the protest), and opposite it the intensity of the protest (the level of disruption to the public). In principle, there is no permission to interfere with one person in order to save yourself from another person. That is what elections are for. In an extreme situation, you can declare that you no longer accept the rules of the game.

But now you too are turning it into either 0 or 100, with no issue of degree. If there is distress that is not extreme enough to throw democracy out over it and maybe cause chaos and civil war, maybe it is still enough to justify causing disruptions

In general, blocking roads is too easy to do and the result is severe. People use it far too much and far too casually. The casualness with which people block a main artery and delay tens of thousands of people—babies and the elderly—and often even cause bodily harm, is infuriating.
Even just the accumulated anguish is enormous beyond measure. In every such significant blockage, there is at least one whole family that drove to an event, got dressed, made themselves look nice, got excited, squeezed into the car, and came back home after 7 hours without the event. Because it is so easy to do, foolish or wicked people do it over trivialities.