Here’s one author’s analysis of BDS. It’s a hatred for middle America and the ‘gall’ they had to elect someone who wasn’t a 60’s style radical:
http://www.talkaboutgovernment.com/group/alt.politics.usa/messages/623416.html
That is a good point that he comes from the flower power age but was not part of it.
Again they cannot understand how someone who was in their 20s/30s during this era and appears not to be influenced by it.