I flew the DC9-30 series for 10 years and it was the best, most fun plane i've ever flown.
here is an argument for him. if slats didn't add drag, then why retract them at all? (slat speeds aside of course) Why did the designers spend all the time and money to make the slats retract?
Now, I disagree with you on the idea of flying clean/idle to 1000'...you can get yourself into trouble doing that. What if the engines don't spool up? WE have a mandatory spool up check at 3000' in every jet we fly.
There is nothing wrong with putting the slats out early...oh sure you might have a bit more fuel used. But, you must ask yourself if you have ever been out of position for any reason and had a go around. If the slats had been out, would things have been different.
In 37 years of flying, I've had one perfect descent situation from cruise. ONE. (in this I mean ATC and everything else worked out). It was going from KCLT to Talahasse florida. I still remember it. But I still spooled up at 3000' because I also know guys who have gotten in big trouble being UNSPOOLED>
so...is there drag...yes
is it wrong...no, it may actually be slightly safer.
should he buy you a beer? yes, but be sure you are at least 8 hours plus prior to the next flight...and it would be healthier if he bought you some orange juice.
The douglas twinjet series (DC9 etc) is a great plane.
Oh, and one more piece of advice...if you are anticipating ice in the descent...start heating the wing up in cruise...even clear of cloud...and the caution lights won't come on in the low rpm range of the engines in descent.
too many people wait till they actuallly get into the clouds/ice before starting anti ice.