I agree that orcs can have good qualities, for example loyalty:
Orcs will often pursue foes for many leagues into the plain, if they have a fallen captain to avenge (FotR 351).
What would be other reason than (twisted) sense of honour, it's like this "they killed ours so we want revenge". Uruk-hai are even more "nationalistic", proud of what they are:
We are the fighting Uruk-hai! We slew the Great Warrior. We took the prisoners. We are the servants of Saruman the Wise:The hand that gives us man's flesh to eat. We came out of Isengard, and led you here, and we shall lead you back by the way we choose.
They have sort of tribal bond, of course they won't hesitate to kill other orcs if they are from different tribe. Among themselves they can be colleagues, like Shagrat and Gorbag talking about ,,good old days", and that they would take some ,,trusty lads" to plunder:
'No, I don't know,' said Gorbag's voice. 'The messages go through quicker than anything could fly, as a rule. But I don't enquire how it's done. Safest not to. Grr! Those Nazgûl give me the creeps. And they skin the body off you as soon as look at you, and leave you all cold in the dark on the other side. But He likes 'em; they're His favourites nowadays, so it's no use grumbling. I tell you, it's no game serving down in the city.'
'You should try being up here with Shelob for company,' said Shagrat.
'I'd like to try somewhere where there's none of 'em. But the war's on now, and when that's over things may be easier.'
'It's going well, they say.'
'They would.' grunted Gorbag. 'We'll see. But anyway, if it does go well, there should be a lot more room. What d'you say? - if we get a chance, you and me'll slip off and set up somewhere on our own with a few trusty lads, somewhere where there's good loot nice and handy, and no big bosses.'
'Ah!' said Shagrat. 'Like old times.'
It seems also that orcs are brainwashed to think that elves and men are more cruel and treacherous than they:
'It's my guess you won't find much in that little fellow,' said Gorbag. 'He may have had nothing to do with the real mischief. The big fellow with the sharp sword doesn't seem to have thought him worth much anyhow - just left him lying: regular elvish trick.'
Of course they didn't rescue from similar situation their fellow Ufthak, just because they feared Shelob.
It's like a stereotypes that were put to their heads to hate every other beings, besides they're evil because they never had opportunity to be anything else. They were always influenced by greater powers, first by Morgoth (who probably presented himself to them as god) and later Sauron (influence was partially magical, the same way as Saruman did with his mind-controlling voice).
I meant nationalistic in positive sense, as a sign of community spirit which in itself is good. Also there is a personal view of author. Tolkien wrote:
"They would be Morgoth’s greatest Sins, abuses of his highest privilege, and would be creatures begotten of Sin, and naturally bad (I nearly wrote ’irredeemably bad’; but that would be going too far. Because by accepting or tolerating their making - necessary to their actual existence - even Orcs would become part of the World, which is God’s and ultimately good.)~Letter #153
"Naturally bad" signifies their natural tendency towards evil, even greater than it is for Men, which is further influenced by the thralldom of higher dark powers and their own culture devoted to destruction, hate and essentialy doing evil deeds for pleasure.
"It became clear in time that undoubted Men could under the domination of Morgoth or his agents in a few generations be reduced almost to the Orc-level of mind and habits;"
It is also known that orcs secretly hate their masters and miserable life they were forced upon.
But ultimately Tolkien foreseen for them a more merciful fate. By becoming the part of the world they had chance of redemption. So while we don't have examples of strictly good orc in any stories, we can't forget about the potential of change.