Needle away. I will be your haystack. (Does that sound naughty? Sorry.) You are right to differentiate between groups by choice and groups by birth. As I was writing the comment above, I was thinking about generalizations such as "Those tea partiers are f'ing stupid."

I just went searching the web to see how I could join the tea party in Succasunna NJ, for example. I discovered a lot of tea parties and they have meetups -- just like Hubskiphiles -- (except more guns). Some groups really try to put the Party in tea party. All the local orgs that I saw had mission statements and these statements were not all the same.

There's a lot of local tea parties, but I doubt everyone holds exactly the same set of beliefs or has the same education or are motivated in the same way by the same fear and the same ignorance (generalizations noted) or by the same love of their country.

You are right that people join organizations mostly voluntarily, but also through coercion or pressure or brain-washing or family unity or to follow a loved one -- and they also quit those organizations.

People go on marches sometimes without thinking through the implications of the group they are supporting. Revolutions can be fun and people like groups. So, yes, I would hold by my statement that generalizations about individuals based on their voluntary or involuntary membership in a group tend to be problematic.