Like most of you said, a raw coin allows you to appreciate the coin as an object of history and art much more than a slab.
I don't have the budget I'd like to have for collecting. Therefore, most of the coins in my collection are raw because they're cheaper and there is more room for grading error. However, if there is a key coin or a high grade coin, I'd buy the slab. This gives me much more assurance that the coin is genuine. On a more superficial level, it protects the big money I've managed to invest into the coin.
As many of you noted, the current market is very picky with regards to grading. Suppose I find a slabbed MS65 but find the money to upgrade to a more eye-appealing coin, I'll want to sell the 65 coin to help pay for the other one. Many dealers/collectors will buy a slab much more readily because of the TPG stamp of approval.
In summary: I go raw when I can. But I go slab when i need to invest my scarce income into that even scarcer coin.
I'm sorry if that doesn't make sense. Remember, I'm a poor college student.