The term "extremist" is used for certain activists whose views skew too far outside of the usual range, although one man's "extremist" are another's "unorthodox" view. Depending on the era, a view may be perfectly reasonable or ridiculous, compare the idea of "protecting the environment" in the past.

Some countries do (or have) crack down on really outlandish views for a time. One country's views may also differ from another.

As a matter of principle, I don't much like terrorists as they operate under the goal of spreading terror. I have strong doubts cracking down on encryption would stop them, as they operate perfectly fine with fairly mundane tools and the "mass-surveillance" machine loses them in the noise.