"I find it somewhat implausible that half the population is dumb, racist and all those other labels. "
No - they aren't.
The answer is very easy: They believe Donald Trump.
Trump has credibility in their minds, and when he repeats the lie, over and over - that 'the election was stolen' - they believe it.
On election night - he literally came out and said 'If you count the fake votes, Biden won' - declaring mass fraud, without any evidence.
His followers believe him.
Contemplate the implications of that.
These people do not watch CNN, they watch Fox, OAN, Breitbart etc. where the falsehoods are propagated, or at least never debunked.
They are simply misinformed.
On CNN they were interviewing quite a number of protesters and unanimously 'they believed the election was stolen'.
A close observer will have noticed that the court cases were thrown out, that Homeland Security and the DoJ cleared it etc. - but that truthful information is not passed on to people in the Trump Bubble.
Trump's base don't get their news from sources that will explicitly and clearly debunk the conspiracies.
It's important to contemplate what this means: it's almost entirely not a political divide - it's mostly a divide based on what the facts are.
Consider the corollary: Trump won the election, but there was point-blank, irrefutable evidence that he rigged it. The DoJ, Homeland Security - everyone - points out his fraud.
Trump could merely deny the allegations, declare that he is 'under attack' and rally people to his cause on Twitter and Facebook.
His followers would believe him.
Meanwhile - how would you feel? Literally the election was stolen by Trump. Point-blank evidence.
Would you hit the streets in protest?
Would you 'occupy DC'?
Millions would be enraged, we'd see protests like we've never seen before.
So just contemplate that a considerable number of Americans are completely misinformed and deeply believe the election was stolen and that the Republic is being usurped.
From that perspective, their actions seem more rational.
I've been watching the right-wing media carefully - and while Fox mostly doesn't openly support Trump's claims, they don't spend a lot of time debunking, and they 'go along with it' in a sneaky way by saying 'Millions feel there was fraud and their voices must be heard' - essentially avoiding taking the position that Fox agrees there was fraud, but rather sympathizing with the angry masses who they darn well know are misinformed.
FYI it's actually considerably easier to 'cast doubt' on elections where there is always some small degree of fraud whereupon the tiniest case can be used as 'evidence'.
This insurrection is not about racism or any of that (these things overlap obviously) it's an election based on Fake News.
I know that HN is pretty serious about 'Free Speech' - but folks - Twitter is Trump's primary tool of misinformation - it's his daily dose of koolaid and falsehoods to quite a few million who absolutely take his word for it.
And finally - the opposite is also true: these followers assume that CNN, NBC, NPR etc. are entirely made up of lies. Nothing on those channels has any credibility in their eyes.
This is a revolution based on Fake Information.