Thalidomide. Regulation prevented thousands of deformities in the US by imposing a proof-of-safety barrier before the drug was allowed to be sold. Other countries were not so lucky as to have that regulation in place.
More to the point... How, as an individual, am I supposed to make an informed judgement about the relative risks of MtGox vs Bitstamp, say? I have no inside information about how those companies operate. There's a huge information asymmetry problem that regulation alleviates.
How does regulation alleviate it?
You would make a judgement based on their website and feedback from sources such as HN, Reddit, Twitter, word-of-mouth, etc. That's how we all make decisions based on nearly everything we use regardless of whether or not it's regulated by the government. And if it's a new service where you don't have access to credible sources, you make a judgment based on the level of risk you're comfortable with.
That's exactly why some people are willing to give emails or phone numbers for 'Show HN' posts on here and others are not. Some don't care so much and really want to try the product. Others want to wait to ensure they are credible.
2. Asking "Who will regulate the regulators" is unproductive. Obviously, human nature wont change, and corruption will always exist. But just because regulation isn't perfect doesn't mean we should throw it out.
Also, you should already know the answer to your own question. By promoting transparency, citizen participation, and establishing checks and balances, we can mitigate the effects of corruption (but not entirely). This has been known for, I dunno, a few hundred years. Are we really debating this now?
Governments regulate things that are risky. It's the main reason we have agencies like the FDA and SEC.
Let people decide what they want to consume.
We already did slavery once, and were likely to continue doing it at the time. We already kept women from voting, and were likely to continue doing it at the time.
And although I personally agree that it shouldn't be the government's job to baby sit people, the country as a whole is currently going the opposite direction with things like the Affordable Care Act and Sarbanes Oxley.