Would have agreed before my last trip. ATC asked us to do 310 on the descent, FO put 310 in the cruise alt line and executed. We started climbing to get to the vnav path. Nice job, Sluggo. And there was one last summer that fell in love with cruise altitude changes instead of just putting it into descent mode, so when they finally gave us descend via the RNAV arv into LGA, he executed "des direct" before I could stop him.

If we were all smart enough to quit making stupid mistakes like these, I would agree.