They will cross, they don't care
It's not that they care.. its unpleasant, it's not easy to walk or drive past a hundred people yelling at you.
Sure people will do it more than once but UPS will have to pay them a lot to make it worthwhile
Quite a few of the older generations make fun of gen z and millennials for being soft but now they are going to have the fortitude to cross hostile picket lines enmass? For a job many of them don't want?
How many doordashers with civics will they need? Not many independent truckers left to move the feeders and why would they drop their current obligations? Unless UPS makes it really sweet.
Same for trucking companies. Why are they going to stop hauling another companies loads to move UPS crap into a hostile strike. A lot of their drivers will not want to listen to the crap and non union companies don't exactly want to expose their employees to unions, you donr think some smart BAs or organizers would try to talk to those guys