Consider what was done to central and South America, the Philippines, and to an extent right here in the US, back before it was the US.

Explorers and missionaries traveled the world, conquering territory, and forcing their religion on the native people. This seems to have been done mostly by Spain, but others like France and Portugal also participated to some extent. Convert or die. Was it officially sanctioned behavior by Rome, I can't say but it went on for hundreds of years so they can't have been too upset by it.

The Philippines is the place that I have the most extensive experience with. They attempted to completely destroy the native culture to the point of even forcing them to take new 'christian' names. Also forcing the religion onto them and blah blah.

As I said in my post in the part you snipped out, it isn't a direct comparison to the modern day Islamic terrorism, but there are several similarities.

Anyone that adopts the join us or die philosophy is fucked in the head, no matter how well intentioned they may think they are. It flies right in the face of whichever religion they claim to serve. But I am no religion scholar or anything.  

You may agree or not as you choose, but there's no denying that it happened. And that it was a horrible thing to do to countless people around the world.