I never said it's acceptable, but as someone who lives in Barcelona, actually sees first hand what's going on there I can see the images in the video with an extra context that a lot of people on internet can't have just by seeing videos from other places.

You've seen in this video a man that got involved with the police and beat up for expresing his disagreement, which of course he's allowed to and he shouldn't be beat up for it, I'm pretty sure we both can agree on that.

What probably you've seen less (or maybe not even at all if you don't even live in Spain at least) is why the police acts like this. Because between the people that do pacific manifestations stating their disagreement with the sentences with separatist politicians, there's some radicals that these weeks attempted (or committed in some cases) to attack government building, there's been some cars burned and hundreds of containers. Those are a minority of people that cause problems and force the police to act so violently and are the culprits of giving a bad image to some of the manifestations that would be completely pacific if it wasn't for these individuals.

Then sure, there's scenarios like in the video where a random guy expresses disagreement doing nothing just because he's close to a conflict area with police acting against these radical group and sure, poor guy got beat up and was harmed doing nothing wrong, evil police, that's what people sees from those videos, but that's why the lack of context makes it look even worse than what it actually is, as it wasn't enough already.

But yeah, ok, I'm an evil fascist myself for pointing the same that other people in the video that were warning him being in that situation and told him to shut up and avoid trouble, not because he wasn't allowed to have his disagreement with the police, but because it really wasn't a great idea in that moment all things considered and agreeing with that people that it was kinda dumb to do so.