Idealists: Believers in or followers of some grandiose vision, usually religious or ideological. Alternatively: believers in philosophical idealism)

There have been many idealists of many faiths and of many political convictions, since there seems to be an innate human tendency to wish to do what counts as good in groups, which also gives such activists the feeling that they are good, since all the people they socialize with share their ideals and want the same, or at least pretend they do.

As a rule, idealists are the dupes or tools of political or religious leaders, and as a rule the greatest harm human beings are capable of is done on the basis of the noblest reasons.

And other names for 'idealists' are: 'enthusiasts' or 'fanatics'. The only known way not to be a fanatic is to think individually for oneself or not to be a follower at all.