There are people who would otherwise support their cause that are negatively affected by dumb decisions like this

(Y) doubt.

The sort of people that wring their hands at leftists peacefully protesting are the same people whose hearts bleed for people who commit hate crimes or vote to dismantle human rights. They're either deliberately trolling or they are victims of propaganda with no ideological object permanence. Either way, you can't convince them by meeting their terms. The troll or the propaganda will move the goalposts, the centrists will follow, and it will be like you never did anything.

Everyone can empathize with people driven to crime because of how deeply they feel the current politics has it wrong. What differs is who people choose to extend that empathy to. If you don't empathize with the left, nothing you hear about them on the news you currently watch will change that. Everything will appear to have bad vibes.

As for the literal effect of blocking a highway for an hour - it causes fewer delays for cars on the M25 than one week of Tory public transit policy. The better public transit, the fewer people need cars, the fewer traffic jams. If such delays are truly unacceptable to you, you should find any candidate that isn't radical left revolting.