It's that blocking traffic is a material, aggressive escalation of a protest that could have very negative ramifications to the cause. Not only does it really really piss people off, it puts human bodies in direct conflict with vehicles and could potentially block travel to someone that needs urgent medical attention.
If that's your jam then go for it. For my part, if i am in a vehicle with family and we are in a traffic jam due to a protest, i'm going to be in an agitated state...not because of the delay but because of the inability to escape. I'll wait it out, but if people start attacking my car and breaking windows, i'm hitting the gas till i see daylight. That innate sense of how i would respond and is why i think people should approach blocking traffic with caution.
He's isn't "firing [himself] up.." as you say, he's thinking out what could possibly happen and considering what his options are.
If you wait until you're in such a situation (people are breaking into your car and threatening to harm the occupants) you simply don't have sufficient time to think out those options - you must think and prepare ahead of time. For those who live in places where riots or firefight break out regularly, this is the proper and usual way to prepare.
FWIW in most of the USA it isn't homicide if you kill an attacker(s), provided you are defending life or limb of yourself, others and/or your property.
jcims didn't say that he would be "Driving a car into a crowd..." as you state.
Clearly, if rioters begin beating a car and breaking windows the driver has the option of surviving by driving to preserve life, limb and property.
jascii says>"mentally training yourself to make that a "valid option" can be extremely dangerous."<
Have you ever been surrounded by a mob or mobs while driving a vehicle? We're discussing it here, so you've now at least considered (and possibly once experienced) such a situation: otherwise how could you claim that such an option can be, as you state, "extremely dangerous"?
Tell us your valuable experiences, please.
BTW there's plenty on this topic previously on the innertubes:
https://urbansurvivalsite.com/caught-riot-driving/
https://www.quora.com/What-are-my-legal-options-if-my-car-is...