Actually the claim is a given (yes, the bar is pretty low when talking about politicians) as conservatives have a ethical code. Sometimes they fail to live up to their code but they have one. Liberals by their very value system don't believe in ethical codes. Look at ANY liberal cause and it will conflict with another liberal value. Their values make no sense. You do need to separate politicians from the general public. Also note that "everyone does it" has been a defensive postion going back to Bill Clinton. When they can get you to accept that everyone does it then they win. You will lump all people together with the slimy even if that person is above reproach. Don't buy into the liberal line.
About ten years ago the liberal Kansas City Star did a report on the graft and corruption in the Missouri state house. They listed the politicians in order of the amount of money or gifts they had recieved. Dead last on the list (meaning the least corrupt) was a republican representative who had accepted a dinner from a supporter and then reported said "contribution" to the ways and means committee! Was he talked about for being 100% correct? Nope, he was still included in the corruption list as was everyone else. The Star did not even consider that some people were not corrupt. According to the Star, they were all guilty to different degrees. By the way, his meal was a small salad worth about ten dollars.