I am reminded by my wife of our niece, who is a year younger than our oldest, having a similar reaction to a family oriented film about which we didn’t give a second thought and neither of our boys had anything other than a pleasant time viewing.
WARNING: the rest of this comment may be a bit spoilery if you haven’t seen the film. I will try to keep spoilage to a minimum.
I see the pattern you layout but in a different context. I interpreted her imprisonment as part of the hero’s journey Susan follows through the course of the film. I think the emphasis was more on her lack of power than any uncomfortable echoes with political reality. Really, her imprisonment isn’t any better than her prospective marriage would have been. None of the monsters are tortured and I really saw General Monger more as a warden than a tormentor. He does go to some lengths to explain the terms of her imprisonment and I thought it was motivated more by public safety than any desire to do harm to his charges. I am not excusing unjustified imprisonment, I just don’t think that was the writers’ intent.
There are no shenanigans when Susan and the other monsters make good on their end of the deal, defeating the alien probe, which I found surprising. An excuse could have been drummed up to return them to captivity rather than giving them liberty to see family and friends. The final scene, after the denouement, also speaks to their own choice to act as Earth’s newfound defenders even if the circumstances that led them to it are, to be fair, originally coerced.
As to stepping into harm’s way, the second time they enter into danger seems to be as much of their own choosing. This was after everyone thought the threat was over and the monsters had been given liberty. Definitely Susan’s choice to save her friends when she could have otherwise made her escape reinforces that. The fact that she effectively triumphs even when made completely powerless in the climactic scene really makes me think the point of the story was more about her being a captive to her own passivity and her family’s expectations even before she was made a prisoner.
Along similar lines to your interpretation, one could make an argument that Colbert’s portrayal of the president was a satire of the Bush regime. The character is laughable but able to do manifest harm, e.g. the scene with the two red buttons. Arguably he is only undone by the sheer depth of his own incompetence. I think while that argument might be made it is a but of a stretch. The ineffectiveness of the executive can be more simple explained as serving the plot by creating an opening for the main conceit of the film, of General Monger’s plan to pit the monsters, which he has conveniently been collecting all this while, against the new threat of the alien invaders.
I can’t make any promises, but I will try to do a more considered job with plot synopsis of family films in future quick reviews to help suss out any issues I may not see as problematic but other families might. I’ll try to add reminders that my standards are set by myself and two older boys so may not be as applicable for families constituted differently, which is I think at least part of the case here, as you suggest.