Maybe Lagat is an absolute POS. Maybe he took drugs, lied about his citizenship and, well I think those are the two main grudges people seem to have.
What if the citizenship deal was so that he could still run even though technically he wouldn't have been able due to pendin paperwork?
We don't actually know any of these athletes the same way we don't know most anyone, not even really ourselves. With Lagat, at least he is nice, not just in interviews, but in how he interacts with other athletes. Also seems to love his family. And because it all looks so good on the surface, I can see where the true tendency to dislike him comes from. People want role models, sure, but sometimes people see someone for whom everything seems to be going right in life, and it pisses them off. They take it as a personal affront, as if this person even knows them or has anything to do with their plight or can have any knowledge of their less than ideal life. Instead they are living their life in its varying shades of perceived self-aware ideal.
Tl;dr just watch his beautiful stride and be satisfied.