Politicians are pure scum.
I must disagree.
Putting "politicians" and "pure" in the same sentence is incorrect usage of the word "pure".
Any of the following may be properly substituted for the word "pure" in your statement; dirty, filthy, obscene, unclean, evil, immoral, corrupt, degenerate, perverted, or damned. Or simplify the sentence to "Politicians are scum" and we'll automatically add one or all of those other adjectives in our minds.