Is it correct to ignore every doubt that arises concerning purity, even if what was ignored actually happened, if the person is afflicted with obsessive doubts about purity?

As long as you are not certain about the occurrence of the matter concerning which you are experiencing obsessive doubts (waswasah), then disregard the waswasah and pay it no attention. This is because Allah has commanded you to turn away from it when it afflicts you. Do not pay any heed to it until you attain absolute certainty.