They didn't "become" violent. It was an organized attempt to prevent the lawfully elected head of state from being certified and overthrow American democracy using violence.
Even the least violent among them committed a felony by entering the Capitol building. That someone else broke the window they entered doesn't make their entry any less illegal.
Inserrectionists who stormed the capitol to take Congress people hostage and stop the vote got distracted by posing for the cameras, taking selfies and casually enjoying themselves
> to take Congress people hostage and stop the vote got distracted by posing for the cameras, taking selfies and casually enjoying themselves
There's no contradiction there, despite your efforts to portray one.
People often take glee in and celebrate violence even as they commit it against others.
The german language has even given us a word for it: schadenfreude.
Thanks to the lies from the politicians and media personalities they follow, primarily the president, many of these people also fantastically believed that they were overturning a fraudulent election, and were therefore celebrating what they thought was an imminent success in that objective.
Even the least violent among them committed a felony by entering the Capitol building. That someone else broke the window they entered doesn't make their entry any less illegal.