How did counterculture change people's attitudes in the US?
The counterculture did not, of course, change everyone's attitudes. However, it did change the attitudes of many people towards such things as sex, drug use, and authority.
The counterculture generally got people to shed some of their traditional values. It helped to relax attitudes towards sex, leading to our current situation in which sex outside of marriage is broadly acceptable to many people. It helped to legitimize drug use in the minds of many, though acceptance of drugs has not spread as much as acceptance of premarital sex. It also helped to make people less respectful of authority. It did away with the days when authority figures were respected and obeyed without question.
These changes did not impact all people, but they are some ways in which the counterculture changed the attitudes of many people in the US.