Perhaps the most telling criticism leveled against Treasury Secretary Henry Paulson’s plan to overhaul the nation’s financial regulatory structure is that it is too big to succeed. His blueprint is sweeping, and size matters when it comes to reform.

The trouble with such bold catch-all legislation is that it catches all — both the good and the bad. Paulson’s plan would mean the elimination of some government agencies and the creation or expansion of others. In principle, there is nothing wrong in this; vested interests often tend to defend the status quo to protect their turf rather than to seek disinterestedly for the best system possible.

Paulson is right, too, when he says, “We should and can have a structure that is designed for the world we live in.” Much of today’s regulatory system was put in place half a century ago or more.

But if it is true that America needs rational, streamlined and efficient financial regulation that is well-adapted to the rapid evolution of sophisticated financial instruments, it is just as true that only what is broken should be fixed. Change is not good in itself; some things change for the better and some for the worse. And better regulation is not the same thing as more regulation. Red tape should be kept to a minimum.

Edward Yingling, president of the American Bankers Association, suggests that Paulson’s plan would weaken American banking by “dismantling the thrift charter and crippling state banking charters.”

Dan Mica, chief executive of the Credit Union National Association, says the proposal to phase out the National Credit Union Administration would force consumers to pay more for less. These are serious criticisms that Congress should meet with equal seriousness.

If ever a set of reforms cried out for real, deliberative Capitol Hill hearings rather than reflexive grandstanding, it is those contained in the blueprint unveiled this week. The nation is beset with financial and regulatory problems, but some of those may turn out to be more apparent than real.

The economic downturn and Wall Street’s concomitant disasters present a real challenge for genuine and substantive reform. But, sadly, they also present a golden opportunity for posturing and cheap point-scoring.

In election season, the temptations of such an issue are obvious. But we hope lawmakers will decide that their maxim should be the same as that of doctors — first do no harm.