1. Well that is overclocking, but it's not overclocked far enough!
2. That applies to any processor. If you want to overclock you have to be prepared to deal with it. If we applied this reason to all CPUs should nobody ever overclock? What if we don't mind the extra heat? What if it's Winter?
3. No you don't have to disable anything, but overclocking uses more power because it runs at a higher speed and voltage. At full load it doesn't matter if power saving features are enabled or disabled anyway, because they won't be active even if enabled.
3.5 (since you edited the original 3) This also can be applied to any processor.
4. I disable an overclock to do my own overclock. Meh.
I have several reasons (but only if I get one):
1. It is brand new.
2. It costs quite a bit of money (of which I have little of in the first place).
3. You aren't sure yet what could go wrong, let others be the bait and see what goes wrong when they OC it.
It would be a waste of time to buy an i5 750 and not even see its full potential... Yea of course you can run it at stock speeds and it should be enough for normally daily needs..... But then again if you buy the 750 just for simple daily tasks then you bought the wrong CPU in the first place....
I am positive that most users that buy such a CPU will be tempted to see what it offers... If you don't want to OC then leave it alone but don't say that it would be wise not to....