Serious protest should involve serious people power, not just a handful of radicals aiming for maximum disruptive impact (usually knowing they'll face zero consequences for it, and may well turn more people against their cause, e.g 'Just Stop Oil' in the UK)
But when you screw around with transport infrastructure, you may be putting lives at risk if emergency vehicles are held up in completely unnecessary traffic jams.
The majority of the time, it's groups doing things like this that lead directly toward what you're calling "serious protests".
Without such groups, nothing would ever really happen. There's an enormous power differential here, and theatrics like this is one of the few ways available to help level the playing field.
I guess, really, my point is a bit broader than "inconveniencing". What seems necessary is attention-getting theatrics that actively angers those who want to maintain the status quo, and the Montgomery bus boycotts were absolutely that.
In this case the argument works both ways.