By the same logic, ff terrorism under the flag of a cause is seen as an effective disincentive for policy change in a particular direction, then we would just have an escalation of false-flag terrorism sponsored by anyone who wants to avoid particular policy changes (whatever the merits) as they adopted the now-proven strategy.

Your position is no less "advocating terrorism" than the one you responded to. The only way not to encourage terrorism is to evaluate policy changes on their own merits, and not be swayed from acting on the merits of the policy changes themselves by the fact that terrorists have stated goals related to those policy changes, either as a positive or negative factor.