I believe I made a post about this a few months back, but there are a few things to consider, I think.
During this time, the cold war was hitting its peak, if not at its peak already, and hippies, for many older folk like Rick, were as anti-western as you could get.
In eyes of the preceding generation, they were no better than communists. They eschewed the occidental ideals of working hard, contributing to society, and making something of themselves. They were anti-establishment, circumspect of the negative effects of consumerism, but blind to the positives of capitalism. In short, they were anti-American, and given that Rick Dalton and the older generation fought for American ideals, Rick saw them as stepping on their sacrifices. In the film, they're freeloaders. Their only visible line of work is providing sightseeing on horseback for tourists, hardly a job that requires much effort. They were against working hard which, at the time, was seen as an integral part of American culture. I reckon a large part of why Americans work more on average than any other nation is because of these instilled beliefs.
The hippies, in some respects, were akin to the millennials, in the sense that they were too young to have served in either the Korean and Vietnamese war or in the Gulf and Iraqi/Afghan war. Although millennials don't have a subculture, they're colloquially and disparaging referred to as such. They were idealistic, and as with many ideals, what looks good on paper more often than not resembles what Tarantino depicted in the film, disarray.