New divers on a boat with experienced divers usually are not well accepted by the 'old timers'. It that same in skiing, no-one wants to have to wait for the new guy guy to make his way with a snow plough on a red run!
The answer? Well what I do is pick sites that I know well, and plan the dive so that the new diver can get a nice dive without inflicting any time constraints on the other divers. Keep the new divers profile more shallow, make sure that he can get back to the boat without sucking his air past the 500psi point, and ultimately become a better diver.
Supplying air to new divers to supplement their original tank is wrong in so many ways. Too many to list here for sure!
I consider myself to be a DIVE PROFESSIONAL and I have a responsibility to provide role model behavior to those diving with me. There is so much PADI bashing around at the moment, and it makes me very cross when I hear things like this being condoned by the dive community... it's wrong folks!
I'm sure that the DM sharing his alt thought that he was doing the right thing. The diver would have appreciated the extra air and the other divers will have appreciated the extra bottom time, and the DM will have appreciated the extra tips! (Objection your honour! Speculation!
As a leader of dives it really upsets me when folks who should know better get their panties in a knot about having to dive with newly qualified divers. I do my best to run separate dives for new folks / experienced folks, but some times its just not possible.
Please remember, we were all newbies once upon a time so a little more support and understanding to the new divers and the DMs / Instructors that are charged with looking after them would go a very long way!