How does politics corrupt you??????

Hearing all theses tales of corruptions of the 'angels'.. what the hell? How does running for a ward corrupt you? You lie here and there obviously, I mean it's near impossible to gain wealth and power 100% legally these days no? But if your intentions are for the common good... what's corrupting you and 'draining your soul'? Are politicians making up this bullshit because they want less and less people running for wards and such?