Here is the problem I see. This ins't a this or that issue, meaning that what I do to assist the crew, does not detract from the job I do as a safety conscentious pilot and certainly safety is the overriding concern.
Since the flight plan is sent to the a/c in adeaqute time, that allows me time to peruse it, note theghlights and query dispatch in case of any perceived issues.
Loading the "box" can be done in minimun time, if one knows how to use it.
While you may not believe it, I can greet every single deplaning passenger, help the F/A's clean and greet every single passenger getting back on. Further, I trust my excellently trained and ultra competent F/O's in getting the clearances via acars, run the performance, wt and balance numbers etc.
As has been mentioned, I think most of us are smart enough to realize, that other functions take predence over assisting the F/A's, be they MX, wx, fuel or all the other funny stuff we deal with on a daily basis. Notwithstanding a few misguided F/A's, they do to.
Helping out the F/A's makes a lot of sense, not just from a team perspective, but if you help the F/A's and make their job a bit easier, they might treat the customer better, which hopefully brings them back to your carrier and hence ensures your paycheck. As much as I hate to say it, most of a pilots finest work takes place behind a closed door and the customer really will never know about it, this is as it should be and while unfair, you are judged mostly on your landing, yep, it always comes down to those few inches, both in aviation and in love
Since the F/A's have the greatest influence on the customers flight exeperience, why not try to assist them, so that they are in a great mood. If you do not make too many mistakes, you will still be the one basking in "glory" as the passengers thanks your for a great flight.
No jetblue pilot I know, would ever let cleaning the cabin interfere with their real duties nor would the company condone or allow this to happen,( or ever question the pilot) but the great majority of them takes tremendous pride in their place of work and realize for better or worse, that their paycheck is dependent upon making the passenger chose their airline over the next one. If crossing a seat belt or two is what that takes, then I think that is a small price to pay!
Ohh, and don't forget that thing that G200 mentioned
P.S. Ask most freight dogs for smaller companies, who exactly loads the freight and what a great flying job they do anyway. Heck, the F/E and I loaded a DC-8 with the assistance of a one armed man, but that is a completely separate story.