I'd be a lot more inclined to respect political careers if politicians actually got shit done more often. It seems to me that nowadays politicians rely more on manipulation via subtle discrepancies in word choice to charge up their reputation than actually getting things done to please the people. They rarely do anything with the citizens at the top of their priority list, and that's a duty that's pretty inherent in the job description.
I think pursuing politics is assumed to be an unscrupulous choice because too few morally conscientious people are ready and able to sack their principles in order to pursue pragmatic compromises--or just straight out lie in order to get elected. Also, politicians are endowed with power and prestige in order to enable them to serve others, but those virtues enable the unscrupulous politician to serve himself; thus, venal people are drawn to politics like flies are drawn to sh*t honey.
Worse, politicians are appointed, condoned, and approved by the people they govern. The more corrupt a people, the more corrupt their politicians will need to be in order to remain in power.