I went to a Quaker college for four years. I'm fully aware they are no longer "plain" and well-acquainted with their beliefs and practices. I have many friends (no pun intended) who are Quaker -- some born into the Society of Friends and some who chose to become Quakers as adults or teenagers.. Some of the people I know now and went to college with came from families who did not dance, drink or smoke as part of their Quaker tradition. We also had Mennonites at our school, but they weren't plain. Some of them did come from those sorts of families though and they didn't participate in the activities I just mentioned either for their religious reasons. Maybe, they were from small and unusual sects or something.
I also know that Mennonites and the Amish do not look identical. Nevertheless, the both have plain sects. Additionally, the strict non-worldly groups as far as I know all place a high value on modesty, they don't play musical instruments and they don't dance. I'm wasn't talking about core substantive doctrine or theology.