I don't think the people saying "protest like the french" are the "liberals" OP is claiming "lost their mind" at BLM. This feels like strawman of strawman.

The people that "denounce violent protest" are people that have never been to a protest that wasn't a planned parade. Violence is an inevitable result of protests because the state itself uses violence to stop the protest. No matter how peaceful its initial intentions of protest are.

A "protest" that has a start and end date coordinated with the state is not a protest. It is a parade.

The majority of what people call "violence" is property damage. Property damage is not violence. But somehow we convince everyone that broken windows are worse than broken bones.

The same people that "denounce violent protest" also seem to have no problem with the use of chemical weapons on crowds of unarmed people. You go out to a protest, the first time your eyes are burning from tear gas you'll understand why any protest will fight back when violence is first placed on them by the state.

Steps to make people watching on TV "denounce violent protest"

(0) Society reaches a breaking point and protest form with the purpose to disrupt the ability of society to operate without acknowledging the injustice the protest is pointing towards. (1) Protest are labeled "violent" because of property damage. Usually with less property damage than the aftermath of the average football match "celebration" results in. But these initially small acts of property damage are the focus of the media. Very little is said about why the protest started to begin with. (2) Police use chemical weapons (banned in warfare) on their own citizens. Rubber bullets, flash bangs, hoses, etc. All acts of actual violence. Don't believe me? Take a rubber bullet to the head and tell me it's not violence. (3) Protesters respond to violence with self defense measures. Kick back tear gas canisters, using leaf blowers, and becoming more defensive in body armor and gas masks to maintain the disruption the protest is meant to create. Yes. The goal of a protest is to disrupt society and inconvenience you. That's the whole point. Stop saying "it makes me not support them when they block the road". Dude, they are blocking the road because you weren't supporting them. Protest is the voice of the unheard. (4) Police work to escalate violence through plain clothes officers working to increase property damage and get crowds of people to reach levels of property damage not intended by the protest. An individual act of violence of a single protestor or act of property damage can be used as justification to use violence on to a larger degree on the crowd. The police goal is not to keep the protest peaceful. The goal is to escalate the violence so they can justify their own levels of violence. (5) Media covers the protest primarily on the property damage and violence of the protesters. The violence of the police is not spoken about. The violence of the police is treated as "keeping order" when it is doing the opposite. All the time we watch media people on the ground not "afraid of the violent protesters" but are literally running away from tear gas and flash bangs themselves. Next time you watch media coverage, watch how the media acts, it's far more telling than how the media speaks. (6) The protest either dies out due to people not wanting to risk their lives as the violence is escalated by the police. OR the protests continue and are primarily maintained by those willing to use violence in self defense.

All of this time. The protestors would leave and allow the disruption to end if even a fraction of their demands are met. Paris protest started because of a failure in the education system. The government would rather spend their money on a militarized police force than on education. That should tell you a lot about the reason why protest became necessary to begin with.

TLDR: There are no "peaceful protest" that are capable of achieving the end results the protest itself is trying to achieve. The state will respond in violence to stop anything that actually has a chance of forcing change. There is no staying peaceful when chemical weapons and rubber bullets are introduced.

How MLK was viewed at the time

i support violent protests. light teslas on fire, raid a walmart, block amazon delivery trucks.

but i don't support, for example, people breaking in and robbing some independent shopkeeper's grocery store. like, those are working class people on your side...

Uh, the Internet is not the problem here. The problem is that liberals in real life work their asses off to make sure that their protests do nothing more disruptive than get people to honk horns. And even THAT is sometimes too disruptive for liberals.