Basically, if the guru is just some slightly weird guy that has some good sense about something, someone who can give good tips on living or is just good at fixing things, then he is fine. If he is telling you to drink Kool-Aid mixed with bleach
so that you can rise as a warrior angel for the war with the Flying Spaghetti Monster against Slenderman
and his army of demonic Bronies
... Either you run or you're on some kind of hallucinogen.