I’m one of the few that felt it was easy to connect the dots on why Queenie joined Grindelwald. The first movie really hammered home the notion of marrying no Maj’s being illegal and this was later expanded upon during the early scenes of the COG where Tina and Queenie have a falling out over Queenie and Jacob seeing each other.

Jacob is reluctant to marry Queenie because he knows Queenie could be imprisoned for threatening the Statute Of Magical Secrecy and she’s very clearly frustrated by the fact that she can’t marry him.

Grindelwald offers her what she desires most. Grindelwald is an an occlumens and so Queenie can’t see through his lies. The line “to love freely” is when he snared Queenie.

Grindelwald’s speech at the end is a massive lie but Queenie buys into it because she WANTS to. If Grindelwald succeeded I highly doubt he’d let her be with Jacob and I feel somewhat confident that the majority of non magical people would be killed under his regime.

JK was showing us how characters we considered to be pure and innocent can turn a blind eye to the evil deeds of someone who offers them what they desire most. Needless to say, we as a species do this all the time. We turn a blind eye to evil acts or acts of corruption concerning politicians we align with but we are quick to point out and condemn those same acts and flaws in those with whom we disagree.