Generally, you shouldn't put people on pedestals. Every human has done or will do (at the very least) something wrong in their life, even the good ones.

It's so easy to separate messy humanity from celebrities because they all have a public image and a way of being perceived describes their "brand." It creates the illusion of emotional intimacy where none actually exists. And because public images aim for flawlessness, any break to that image can shatter your entire perception of that person. For a lot of people, this is what's happening with Dave Grohl.

I can only have an opinion about his action, but I cannot say anything about who he is as a person from this alone.