As usual, the truth is somewhere between the extremes. The "TBS is everything" crowd neglect to account for the fact that we've abandoned TBS for aviators at various times in our history and have done just fine. It's the same thinking that makes us require all Fwd Air Controllers be aviators. We think that there is some Vulcan mind-meld going on between air and ground because of the common training. It really isn't so. BTW, a good way for the Corps to fill its pilot requirements would be to allow enlisted FACs.
However, that's not to say that there isn't considerable value added in having common training between ground and air.
To help out "Ordinary Guy:"
a) Probably the biggest thing that a pilot gets is an understanding of ground scheme of manuever. Understanding what a ground force commander intends to do helps maximize one's SA when all goes to crap. Knowing ground terminology doesn't hurt either. I have had to alter the insert LZ on the fly a couple of times, and it doesn't hurt to understand what the guys in the back need, because there's only so much they can see out the side windows.
Also, Marines tend to put aircraft, especially helos, in forward areas. It helps to know how to defend an area, set up a perimeter, and so forth.
b) TBS isn't the only way to get that knowledge. But it's kinda like Wal-mart: one-stop shopping. You can acquire this stuff on the fly, but you're more likely to step on your crank doing it.
c) An A-10 can support ground troops. He is aided by having a fantastic CAS/FAC(A) platform. However, there is value added by TBS. It's not an all or nothing proposition. Remember that Marines fight as a MAGTF (Marine Air-Ground Task Force), meaning that air and ground are in the same unit. This also means that an aviator may be leading a unit that is mostly ground. It definitely helps to all be on the same page as a unit. Fighting as a unit also helps cohesion, sychronization, etc., etc. E.g. those guys needing a ride aren't just another bunch of losers needing a taxi service, they're from MY battalion.
Long story short. A couple dozen guys w/out TBS is no biggie. We're AT WAR. Get the sand out of your c)(ts about sailors who haven't done TBS/OCS taking your slots. They never were your slots. Repeat these phrases 100 times: "Needs of the Marine Corps," and "Mission accomplishment." At the same time, I hope that if this all happens, we will be able to resume business as usual ASAP and fully train everyone.