Lets say I am looking for a PVP fight (human form or invading).
No matter where you are, its going to take some waiting/searching.
So eventually you find an opponent/s.
If the opponent or myself were to run in a do a one hit kill backstab during a gesture...
Then all we have accomplished is removing the opportunity to have a PVP fight.
And we are back to waiting for a PVP fight.
And that is why I do not do gesture backstabs.
What I do tend to do is stand at a distance and copy what the other guy/lady does (especially 1vs1).
If they start a gesture or do a rapid block I try and do one as well.
If they rush me or cast a ranged spell, then I know the fight is on.