I have 3 .308s, a National Match M1A, an L1A1, and a scouted Chilean Mauser. I also own a .22LR, .223, a .357, a 9x19, a .45 ACP, an 8x57mm Mauser, a .30-06, and (soon) something in 7.62x39. The REAL reason for them all is that they're fun to shoot. The secondary reason is that among this diversity of rounds, I'll probably be able to use most scrounged ammo, and not have to exhaust my stockpiles so rapidly. I'd probably add a .243, a.30-30 WCF, and a shotgun or 2 in gauges besides the ones I have now, if finances allowed.
If, by acquiring other desired firearms, one owns guns which will do what the .308 will do, a .308 in any configuration is probably not needed. The owner of a .243 doesn't REALLY need a .25-06, and a .270 Winchester shooter won't gain much by obtaining a 7mm Mag, assuming one has adequate ammunition stores, or the means to create them. The same may be said of larger bores anywhere but Africa. The owner of a .358 Winchester or .35Whelen can do most anything a .375 H&H shooter can, except bruise his shoulder quickly.
The BIG selling point of the .308 to me is, if the shooter is up to it, he may engage multiple creeps effectively at ranges beyond which the .223 & 7.62x39mm "battle carbines" begin to lose their effect. I would not try to sell the virtues of a .308 in any form to a skilled and experienced Garand shooter, nor to owners of major caliber turn-bolt rifles that are well and truly set up to shoot accurately, continuously, and under conditions far more adverse than those encountered for a short while in a deer-blind (semi-scouted Mausers, Enfields, and Mosin-Nagants come to mind).
I don't know that one MUST own a firearm in .308, anymore than one MUST own a cell phone, motor club membership, medical/dental insurance, Epi-pen, or well-trained guard dog. I DO know that times of adversity are usually better navigated with these items than without.
The shooter's proverb, "Beware the man who owns only one rifle. He probably knows how to use it (for everything)." comes to mind.
