Anyone who takes out churches, abortion clinics, government buildings, schools, etc. It's a very long list of nutters and your kind is not exempt. If you were an honest person, you'd know that. Why do you think the government watches all of them, are they just bored?No, but you often have to adjust society to deal with significant or even not so likely threats. You can make everyone take off their shoes at airports. And you can make them register their guns so you know who might be totally bonkers.
And what religious "extremists" have been a threat to our "society" who are not ... wait for it ... Muslim?
Churches? Are you referring to racists? What does that have to do with "Christian extremists?"
Abortion Clinics - Your best example, happened primarily in the 90s and most of it was against property. Even among extreme Christians they are considered nut jobs. This is a very specific case. It's a data point, but way short of supporting your sweeping statement.
Government buildings - McVay wasn't a Christian and didn't do it for religion. So you are referring to what exactly?
Schools - I'm only aware of Muslims doing this, you're going to have to be more specific.