@Arkhandus
Lots of words that could have been saved, because you're starting off wrong in your first paragraph already. Allow me to quote from the text passages you mention, okay?
Summoning: A summoning spell instantly brings a creature or object to a place you designate. When the spell ends or is dispelled, a summoned creature is instantly sent back to where it came from. but a summoned object is not sent back unless the spell description specifically indicates this. A summoned creature also goes away if it is killed or if it's hit points drop to 0 or lower. It is not really dead. It takes 24 hours to reform, during which time it can't be summoned again.
Player's Handbook 3.5, p. 173
Summon Monster: This spell summons an extraplanar creature (typically an outsider, elemental or magical beast native to another plane). It appears where you designate and acts immediately on your turn.
Player's Handbook 3.5, p. 286
I'm sorry, but claiming that you don't get a real creature is but the clone-image made of energy that simply winks out of existence, at best, a houserule. Both descriptions state that you get the real thing, a solid, living creature from another place that can be reduced to below 0 hitpoints, and, more importantly, killed. This neat little let's-calm-down-all-animal-loving-12-years-old "It is not really dead" fog-up is a laugh if you look at the sentence directly before it. It can be killed, but it is not really dead? [sarcasm]No, hon, it's gone to puppy heaven, where it will find lots of trees and juicy bones.[/sarcasm] A creature, under D&D rules, that is reduced to -10 hitpoints is commonly referred to as dead. Just because it is revived perfectly 24 hours later doesn't mean it wasn't killed, and wasn't dead in the meantime.
And what constitutes as "simple logic" in fantasy settings where gods send their servants off to war against the forces of evil, and them obeying, knowing that they risk their lifes, is up for interpretation. I'd say D&D is modeled on a setting mindset where risking your life willingly for a good cause (to fight against evil) is percieved as good and heroic, while surprisingly being killed by an ally for no real reason is percieved as the deed of callous and evil minds.
@Karinsdad
The "bizarre" reason why I keep ignoring your weird claim in addition to your comparison to a coma/sleep comparison, is that the creature can be, and for an AoO+Cleave combo, has to be killed. It doesn't get any clearer, does it? You kill it, reduce it's hitpoints to 0, drop it with one hit. 24 hours later, the remaining effect of the summoning magic will revive it, yippie. It was dead still. Your sleep comparison is complete nonsense. If you want to compare it to something, you can compare it to somebody laying a Contingency coupled with a True Resurrection upon his slightly dim-witted henchman, because he plans to carve him up in combat later and doesn't want to miss his services afterwards. That way, you can kill the poor sod and still claim it wasn't too bad, because he'll come back in a few.
As I said, that's a course of action that can be viewed as unproblematic only in a very specific set of circumstances, at least from a good character's point of view, without threatening to start an alignment shift.
About my "argument" that summoned creatures don't mind getting killed by their allies because there's some contract between the caster and the highr powers making them "his slaves"...read the spell description. They attack his enemies to the best of their abilities. If he can communicate with them, he can make them attack some other enemy, not attack, or handle some other task he has. They also will act normally in the last round before the spell ends (which, for nearly any creature, would mean attacking the bugger who tried to lop my head off, or flee as soon as possible).
Summoning a creature is the magical variant of drafting a soldier, or hiring a mercenary. They are there at the right time, they fight for you because they share your view about your enemies and want to get rid of them as much as you want it, and they accept the risk of getting killed by your enemy in the course of that, or their superior who allowed the design of that spell accepted it and they obey that contract.
Heedlessly killing off your allies for a small advantage still registers as non-good in my books. If the situation is right, it might be different, but most of the examples given in this discussion simply show that respect for life apparently only counts as good if you can't repair the damage again afterwards for a lot of posters here...which is quite a sad view on it, to be honest.
And yes, I'd have used them to spring traps, fill up a pit so I can walk over it or as bait for an AoO+Cleave combo without a second thought from me and my DM...15 years ago, when I didn't care to think about deeper consequences and did view those creatures as simple cannon fodder, too.
Edit: Make that True Resurrection