I think you know too little about them.
Only people who know nothing about the Amish/Mennonites would be creeped out. I've lived near them my whole life and they are, for the most part, fine people.
I've been up to Lancaster a couple of times and met some of the Amish. They certainly have a lifestyle that most of us would dismiss as too simplistic, but they are generally happier than a lot of us are. I fail to see how anyone would consider them to be creeps.
One of the horrors of all this is that this is the last place many of us would have ever thought a tragedy like this would happen.