Lobbying is bad because it sends people to jail, like Abramoff, Republican Congressman Ney etc etc.
Lobbying is bad because it makes people lie, for example, lobbyist Abramoff made some in the White House lie as to how many times Abramoff was able to meet the President. Was it zero as was initially claimed or was it way too many times as was later suggested...
If you need to fill your paper with more information, you can mention how the American Medical Association, AMA, has a tight grip on the Congress and how it has kept the number of doctors in the US low so you pay more for their fees. You can also add, well, If your teacher is more pro-US than s/he is for Israel, then you can say how the Israeli lobby cons money out of our treasury to the tune of 5 billion dollars a year, every year. The same lobby has stifled the throat of civil liberties in America with the passage of the Patriot Act and the Military Commision Act of 2006.
For the above reasons, lobbying is bad. Good luck :)