Trump needn't be arrested for these things to happen, pulling passports of flight risks is SOP.
I agree 100% that he doesn’t need to be arrested for that. But if he is arrested, it removes all the derp arguments. If Trump is not arrested, the derps are going to be sputtering and saying “but, but, but, you can’t do that. Don’t you know who I am? .... etc. By arresting Trump, it completely neutralizes all such objections. It completely neutralizes all excuses for riots. (Not that it would completely stop any riots.) It makes the “optics” of arresting derps 1000 times less inflammatory.
Trump didn’t need to be impeached. Trump didn’t need to be censored. MAL didn’t need to be raided. Lots of things didn’t *need* to happen. But the fact that they did changes the “optics”.
JMO. YMMV.