My crystal ball says you grew up in an environment which was more conservative than the one you found in college. It is likely to be a frequent case in the US because of the large geographical/political division (in most European countries, distances between areas with different political bents are always smaller), because of extreme situations such as people growing in very-isolated family groups that they need to abandon before they can even think of college, and because both in the US and in other countries, if you’re from a liberal background you’re unlikely to pick a college known for requiring female students to wear ankle-length skirts. It can happen, for example when it happens to be the best school in its field. Opus Dei-owned University of Navarre used to be the best medical school in Spain and to have such a policy; they don’t require female students or workers to wear skirts any more and in fact trousers are now recommended, after some incidents with dementia patients.
Hmmm, I’ve been to a fair few rallies, especially in the last few years, but I don’t know anyone who’s been arrested at them, or burned stuff or stopped traffic at them. I don’t take off time from work for rallies and don’t object to giving up some of my free time a couple-few times a year to stand up and be counted, but I don’t do risky and destructive stuff as part of my protesting, and neither do the overwhelming majority of the other folks I see at rallies.
So I think that the people you’re talking about are quite a small minority of all those who can be described as “white liberals”.
I also think there’s probably not much correlation between having a family/house and not going to demonstrations: most of the people I see at demonstrations likely have families and houses. (Many of them in fact bring their families along to demonstrations, although you’re probably right that the established and older family-type protestors are less likely to do seriously dramatic and dumb shit such as setting things on fire.)
I suspect that people who aren’t really interested in demonstrating for a cause, or don’t really care much about the cause in question, use their domestic responsibilities as an excuse to avoid participating, rather than being actually prevented from participating by their domestic responsibilities. Many people with families and houses will frequently take several hours of their leisure time to go gaming or hunting or shopping or watching sports, after all. We make time for the stuff we care about.