Really, the only people who go against this are the villains. The younger generations (the Air Kids, the Brothers, even Asami) who never had to live with Aang also tend to be more ready to face problems.
I don't think that's just because they didn't live under Aang but is also because they're younger and more idealistic when it comes to solving huge problems. The adults are more likely to be skeptical that their intervention will actually make much of a difference than the young adults/kids are.
(Of course, there's also the fact that the kids are the main characters, so they have to be the ones to save the day, but that's not as interesting of a discussion.)
As for Su, I think it could be interpreted as putting Zaofu's needs above the rest of the Earth Kingdom's. Things are fine in Zaofu, and since it's ultimately that city that's her responsibility, not the rest of the EK, she doesn't want to open up the possibility of bringing trouble to it. Whether or not that's the correct decision is debatable.
I could also see it as her just not thinking she'd make a huge difference in the situation, and to be honest, I'm not sure she would have. At least not any more effectively than, say, Korra or many of the other characters. Su has experience running a city, sure, but there's not really evidence in the show that she'd be effective at handling the larger problems facing the Earth Kingdom at that point in the story. Running one city populated by people who have chosen to come live there because they like your philosophy is a lot different than trying to band an entire kingdom back together after an uprising.
And dealing with individual groups of bandits one at a time wouldn't have made the overall situation better in the long run either, whether or not those bandits were Kuvira's doing.