Can a Buddhist be a problem?

For my discourse community I research Zen Buddhism. While studying and participating in the ceremony I seriously found no flaws in this practice. Zen means "to mediate". How can meditating be a bad thing? They were not extremists, so I can't say that their practiced interrupted their daily life. Also, how can people who are all about peace and unity between nature and themselves be a problem to others? A you guys can see I'm having a tough time trying to found problems in this practice.