My throttle works its way back too, but I quite like it....
If I was to go overboard, and the killcord didn't do the job, at least the boat would eventually come to a slow pace rather than just dart on. Also, if it's rough I don't tend to take my hand off the throttle anyway so it doesn't bother me.
Mine is a side mounted throttle control unit, and tightening the screw does stop this issue in my case, and it doesn't make the general control too stiff either. It's set so the throttle gradually comes back, not quickly, but over a period of time.