One of the better parts of a very uneven movie was how well they had Grindlewald misrepresent himself to the Wizards who came to his rally. Instead of having him reveal his true beliefs, they gave him a mixture of genuine foretelling of the future, and the sort of noble-sounding weasel words that politicians use in real life. Because yes, what he said was so vaguely plausible sounding that someone who was in a mood to hear what she wanted to hear... could convince herself that he might help her marry a muggle.
However, I think the re-introduction of Queenie and Jacob wasn't well done, like I said this movie wasn't all good. Yes, she was miserable and desperate, but you'd think a desperate person would be there demanding to know whether they could get away with a mixed marriage in Britain, and if not there, then where? That'd be the sensible way to cope with their dilemma, go somewhere they could be together! Having her hex him was ridiculous.
Grindelwald was a known terrorist and villain *before* the rally.
The film didn't convince me that he could sucker good wizards into switching allegiances (unless those wizards had been living under a rock).
I expect most of the wizards who came to hear Grindlewald knew exactly what he was about and agreed with his nastier aims, and were happy to hear him sound noble because that made following him more socially acceptable. They'd leave and tell their fellow wizards that Grindlewald was trying to prevent the muggles from starting another world war, not that they were about to start a campaign to subjugate and slaughter muggles.
That's how politics works in real life, after all. People keep quiet about their more evil goals, except among those they trust.