Romney recently suggested that political contributions by teachers should be limited because they have a vested interest in a certain result.
Occasionally there are narrow-point things politicians say where I agree with them in principle, provided they'd be willing to apply the point broadly; usually this is on issues of political balance of some kind. In this case, I'm happy to have Romney open a door that I worry republicans generally leave shut; that of undue influence in politics (Buddy Roemer is another Republican who's talked extensively on this, but he's too moderate to ever have a chance of getting a nomination). Limiting *only* teachers in their contributions is undesirable because it upsets a balance in an arbitrary way, but there's a general good principle of jurisprudence at stake here; people and groups that are disproportionately affected by policy in a monetary way are often not the people you want using their funds to shape the result. As such, if we'd be willing to also limit wealthy businesspeople, groups such as the various chambers of commerce, and so on, from campaign contributions, that'd be great. If we took this further and limited everyone's ability to put more than a certain amount into politics (maybe a yearly limit of $100/person per political division, a la city/county/state/federal), it'd help limit the excessive influence the wealthy and/or the vested have on our politics.
I get that unions are occasionally harmful and/or keep the status quo when change is needed, but I believe they are also generally positive in protecting the welfare of those they represent, particularly WRT labour standards but also wages. Teaching should pay a lot better than it does now in the United States, and it should probably be differently structured.
I doubt Romney is willing to tackle broad problems of overinfluence of wealthy people and corporations though, so in practice while I think he's potentially right on this point, I would oppose putting that conclusion into practice unless it were somehow included into a more comprehensive reform.
(When I was in high school, I once got into a flaming row with a close friend over a political matter; I argued that opening the draft to women was undesirable because nobody should be drafted, so even as I didn't support the status quo, expanding the draft felt like expansion of an injustice rather than lessening. I disagree with my former position nowadays, but the idea of the importance of how legal reforms should be put in order while doing evaluation is an important one)