Corruption in politics is hardly limited to lobbying. Although lobbying is indeed one of the most corrupt practices relating to government, government and corruption seem to go hand in hand. For example, corruption exists in campaign finance contributions, the earmarking process, and in the vote trading process, just to name a few other than lobbying.
The United States legislative system is rife with corruption because the exchange of money and favors sometimes encroaches upon the objectivity of the people making and passing laws. Lobbyists are the vehicles of a lot of the backhanded bargaining that goes on in the House and Senate, but they are not the sole sources of corruption. Often, lobbyists are used as middlemen for executives and corporations who wish to influence lawmakers. Both the originator and acceptors of bribes are just as much to blame as the lobbyists who deliver messages.