A chain split would mean a severe usability reduction. Every user that uses a certain number of Bitcoin services (e.g. exchanges, merchant sites, remittance services) is deprived from using a part of them in the case of a chain split if he doesn't want to use both chains.
I don't see why. After all, a chain split doesn't "halve" the users or the coins: the old chain remains exactly as it was, with all the holdings etc... and all its functionality, and all its users. Of course, if the old chain loses traction, then of course, it will lose out to the new chain - but I don't see the difference with an alt coin.
The difference is that the altcoin is visible from the start as a clearly separated ecosystem, while in the case of an chainsplit that is not so clear. In every chain split there will be services that were available to the users of the existing chain that limit themselves to only one chain (because of ideology or practical considerations). So it's most probable you, as an user, couldn't use all the services you were used to after the split, because otherwise you would have to use both chains.
I don't understand that argument. After all, the original chain is still functioning. How would services "disappear" from the original chain ? You can entirely pretend, as a holder of the original token, that the new fork doesn't exist - apart from the fact that there's now more competition in the market of course. But in what way would a service that was working on the original chain, cease to exist because someone is making a new chain somewhere ? Of course, it could be that the service provider makes up his mind to CHANGE his service and not offer it any more to the original chain - but that's an active decision on his part. He could make the same decision without the fork: giving up on the service all together, moving his service to litecoin, or to ethereum or whatever. That's healthy competition in the market, but it requires an active decision on the part of the service provider to give up on the service on the original chain.
In addition, there is the value/price problem. Money is useful because it's an unit of account. Even now without chain split Bitcoin is volatile, but at least for short-term operations it is usable. What would you do as an user if the chain splits and you have to care about the value you posess? You would have to sell your holdings on the chain you don't want to use anymore (e.g. because of there are no services that support it) on an exchange. Even if the prices of Chain A + Chain B reach the price of the old chain, it's a major usability hassle to have to worry about that.
That is exactly one of the problems of "collectibles" which aren't collectibles, because, exactly, they can be copied over. If a chain had a value-regulation system, then after the storm is over, the value would go back to whatever it was supposed to be regulated to.
As I pointed out in my answer to coincube, the forking business hasn't really taken off yet, but is a phenomenon to be expected in crypto space. After all, it is way easier to give yourself an existing ecosystem than wanting to build one from scratch. There's no reason why in the long term, cryptos will not split regularly.