A piece of formal writing

One of the main causes of prejudice is ignorance. Often, people tend to have preconceived ideas about things they do not really know much about. For instance, people supporting a/the ban on immigration are often those who have never actually had any contact with people of other nations nor have any ideas of what are the reasons forcing immigrants to leave their countries and seek shelter in distant lands.

1. Add a comma between "often" and "people."
2. Probably rewrite since it sounds a bit off: "...about things they don't really know about." / "...about things they don't know much about."
3. Add "a" or "the" between "supporting" and "ban."
4. Again, probably rewrite: "...nor have any idea why immigrants are forced to leave their countries and seek shelter in distant lands."

Keep up the good work!