Activism, in a general sense, can be described as involvement in action to bring about change, be it social, political, environmental, or other change. This action is in support of or opposition to one side of a controversial argument.
There are many different forms of activism; a select list follows.
... and doctors charge a lot of money for their services. Quacks can easily undercut them, by providing what they call, a better treatment for much less money.
Quackery ...