Business, private security, etc will always be corrupt. Always. People are people. Doesn't help that corporations are also bigger people. Taxes are the only practical weapon the common voter has against corporate overreach. What's your solution if we don't fund a group to watch them? We shouldn't just force agencies to spend our taxes wisely, but also demand how and to whom we allocate those taxes to.
This is the other kneejerk response to any suggestion of reduced government spending that needs to die forever.
1 - How about we cut government spending in some are other than the tiny percentage spent on protecting people against corporate abuse?
2 - We have a system in place for this. The problem with it is not that it's underfunded, but that it's been corrupted by the very corporations it tries to regulate! Arguably, stuff like the DMCA shows that more harm than good is done in some areas, thanks to this. This is perhaps the most serious problem in internal politics in America today but it's not in any way a funding problem.