Often, no. The reason for this is because many of the tactics involved in activism are already against the rules. Also, some activism is political. If you can be an activist without breaking the rules, go for it.
Additionally, please avoid unfounded accusations, false claims, and lies in your activism. Please use sound reasoning.
If the thread is not an activist thread, please don't turn it into one.
Some kinds of activism are explicitly allowed elsewhere in the rules. See the rules about politics (with regard to organic gardening).