I view ICS the same as the 'God-mode'-cheatcode in Doom (or similar games). There are people who love to use a cheat and win so let them! This is a SP so if people want to win by using cheats what does it bother me?
I don't understand those people that use this cheat and then whine about 'the game being too easy'QFE
ICS is not some obscure gamey cheat (like say perpetual anarchy in Civ4) that is not obvious and is some kind of overlooked loophole. Rather it is the actual gameplay itself as designed! It is here because of the way the game mechanics work and the balance in terms of cost/benefit of growing large cities vs founding more small cities. It is actually what the game itself is telling you to do! It is even what AIs do!
You start playing a few games and realize that growing cities to make them bigger is very slow after fast initial growth. And then it also becomes obvious that even if you could make those cities bigger with more high level buildings, those buildings take too long to build and/or just don't offer enough benefits for the cost (in time and/or money) vs just founding new cities.
The game also makes it obvious that small cities grow fast and are fairly productive quickly. Yes there is the negative "happiness" hit but there you see that with a colosseum and later SP, they can at least be happiness neutral and self-supporting as long as they don't continue to grow beyond 4 or so. Thus you want to actually purposefully keep them small which is just completely bizarre.
Even if you choose not to go ICS full-scale, it becomes fairly obvious that it just doesn't make sense to try to expand vertically rather than horizontally. And whether you choose to do ICS or not, it is really the symptom of game mechanics and balance which IMO is flawed.