So you can fall victim to the protester's propaganda instead of the mainstream news propaganda?
That's a common argument for many things, and I don't consider it valid.
It is like saying that you can't understand a cult unless you become part of that cult. Some people took on the advise and become brainwashed like everyone else, it is hard to keep a neutral point of view under the peer pressure such meetings usually entail. "seeing for yourself" to get an unbiased opinion is easier said than done.
You mentioned fascists. Did you go see fascists? I did, and they are probably much friendlier than you imagine, and they have convincing arguments. It requires some amount of detachment to see the flaws in their ideas.
Now back to the yellow vests. I've seen protests, my father was part of the movement, I met many people with different ideas. And from my experience, that's a mess. My father joined the movement because of a dislike in the banking system and Macron's administration, and found like-minded individuals. He left a few weeks later when another groups pushed ideas about unions he didn't share at all. I know one self-employed nurse who was booed at a protest when other people from the same movement claim they support self-employment and better medical support... go figure. The things is: individual groups know why they are upset, but the movement itself is all over the place. There are some common themes like taking money from the rich and giving it to the poor but as the movement progresses, it becomes broader and broader, covering immigration (more immigration control, but treat refugees better...), organic food, etc...