Sure, $6 billion looks like a lot of money. But it's a drop in the bucket compared to the rest of the Carrier Battle Group. You need a lot of ships to properly protect a carrier.
Sure, in a conflict with a major international power, our carriers won't stick around. But first, 48 hours is a long time in the context of modern conventional warfare. Guerrilla warfare lasts as long as the people involved want it to last, conventional wars are decided in time periods measured in hours. So a carrier battle group isn't particularly vulnerable. Sure, new tech like ASBMs will force us to change tactics, but we're developing new tech too.
Also, nobody is predicting another war with a major international power. The game changer isn't carriers and hasn't been for decades. The game changer is nuclear weapons. If Russia or China decides to target our carriers, the response will have nuclear components. Nuclear weapons are the only things keeping our carriers afloat anyway, if they didn't exist, we'd have scrapped them a long time ago.
So, 48 hours. During this time, each carrier, with it's compliment of an entire fighter-bomber wing, has destroyed much more than its share of enemy military targets. Also, the battle groups don't have to actually see battle in order to be useful. A carrier is essentially a floating air base that we can put pretty much anywhere we want, giving us the global strike capabilities that make it so, if we have to threaten a petty tyrant with utter destruction, he doesn't just laugh us out of the room.