There are two things that determine every decision we make -
The need to gain pleasure - and the need to avoid pain.
I'm afraid you're right that some may gain pleasure from viewing these videos (as sick as that may be) - however, on the other hand - we don't change or cause change unless and until the pain becomes too great.
The videos cause extreme pain and anguish, and will eventually inspire enough people to rid the pain through more drastic action.
BTTT
The main group of people who will be inspired by these terrorist propaganda videos are other terrorists. The terrorists want us to promote and view their obscene video because it benefits them.