OK, so he was caught soliciting sex in a public restroom. Not so good. But compare that with behavior by other Senators that is not leading to any resignations:
(1) Violating their oath to uphold the Constitution, by voting for legislation they believe to be unconstitutional, but arguing that they will let the courts sort it out.
(2) Voting to delegate massive legislative power to the executive branch, so they can claim credit for the feel-good nature of vague but popular legislation, while blaming the executive for its actual implementation.
(3) Voting for legislation that neither they nor any of their staff have read in its entirety, if at all.
(4) Providing costly earmarks in legislation to campaign contributors and local interests (in violation of Congress's constitutional duty to tax and spend only for the "general welfare").
(5) Accepting various forms of low-level graft that fly under the ethics radar, such as use of campaign donors' vacation homes and airplanes, family vacations disguised as fact-finding trips, spouses employed at inflated salaries by friendly interest groups, etc.
(6) General demagoguery, e.g., Democratic members anytime Medicare or Social Security reform comes up, and Republican members on federalizing criminal law, the War on Terror, flagburning, etc.
I could go on, and I'm not even considering Senators' support for legislation resulting in massive violations of Americans' rights (McCain-Feingold, the War on Drugs). Compared to the every day malfeasance by Senators, accepted as business as usual, I'll take a misdemeanor sex scandal any time.