We often associate corruption with ill-gotten gains. But corruption refers to more than bribes and illicit payments. To corrupt a good or a social practice is to degrade it, to treat it according to a lower mode of valuation than is appropriate to it. Charging admission to congressional hearings is a form of corruption in this sense. It treats Congress as if it were a business rather than an institution of representative government.
Cynics might reply that Congress is already a business, in that it routinely sells influence and favors to special interests. So why not acknowledge this openly and charge admission? The answer is that the lobbying, influence peddling, and self-dealing that already afflict Congress are also instances of corruption. They represent the degradation of government in the public interest. Implicit in any charge of corruption is a conception of the purposes and ends an institution (in this case, Congress) properly pursues. The linestanding industry on Capitol Hill, an extension of the lobbying industry, is corrupt in this sense. It is not illegal, and the payments are made openly. But it degrades Congress by treating it as a source of private gain rather than an instrument of the public good.