Most arguments stem upon some conceived notion upon how a DM prepares a challenge for a party. I hardly think one or two PCs with immunities or hinderences ruin an adventure path or obstacle.
It can, and quite easily. You have to take the Warforged into account, you can't just throw them into anything and expect them to work as well as any other race. They're a special exception to rules. They have to sit at the forefront of your mind.
Fer'instance, consider an adventure on a sailing ship that is raided by pirates, where a big fight is to take place on the rigging of the ship, with Balance checks and Trip attempts and Bull Rushes -- big, epic, ship-top battle, everyone's affraid of falling into the water below...
Well, except the Warforged. Knock him into the briney deep? "*sigh* I walk back to shore and wait for them to pick me up." Or at best "I'm making a few swim checks, but this armor check penalty and weight problem means that I can't actually make any of them, so I guess I'm sinking to the bottom of the ocean where, uhm, maybe I'll die of pressure?"
Suddenly, the entire adventure is derailed while you deal with what happens to the warforged at the bottom of the ocean. One character, one player, cannot enjoy the dynamic ship-based adventure like everyone else. Knock anyone else into the water, and it's a sign of tension, of building drama. The fighter has to take off his armor. The wizard has to make those difficult Swim checks. Maybe they both have to deal with swimming pirates. Goodness gracious me, will they survive? With the Warforged, you better have a back-up plan for when he's just taking a stroll among the coral!
Or consider an adventure into the steamy jungles where Yuan-ti assassins lurk, their poisoned blades piercing deep into the viens of those whose empire they wish to dominate. The entire party is on edge. The cleric has prepared a battery of anti-poison spells. The dwarf takes point. They are struck! Oh noes! Crits and Con damage and Secondary Damage Oh My! Can the dwarf keep rolling lucky? What happens if the cleric runs out of spells? Aiee! Stay away from the sorcerer!
vs. having the Warforged in the game...suddenly, you've got someone who faces virtually no danger from this combat whatsoever. Again, you have a bored player who just walks around and tries to hit things as well as possible. What strategy? What needs he to fear from these assasssins? He's immune to their poison, he's got protection from their crits, he's got DR, so blowdarts are no danger...he's a walking hulk! He's powerful! And you went and had this cult be the main enemy for the adventure, planned out most of the encounters with these guys, and this one character is going to breeze through it like nothing.
Or consider a party of limited players. One person wants to play a warforged. Who gets stuck with Artificer Duty? Who's destiny is it to spend his time not calling down destruction from heaven, ripping apart space-time, becoming one with the shadows, or flashing blades as fast as light, but as the healer and gold-suck-pocket. What if there's only three party members?
Having Warforged changes the way you need to play and think about the game in a way that Shifters and Changelings (for instance) do not.
If half the people are saying he's too weak and half the people are saying he's too powerful, that's not a sign that he's well balanced. That's a sign that he's extreme, he's a violation, he raises red flags on both sides. In some circumstances he's unstopable. In others, he's helpless. This isn't good game design. This is "flaws and benefits" all over again. This is the same problem that afflicts most high LA monster races, but at a lower level so it's less noticable. It's Paper Tiger Syndrome, but when the difference between the mightiest and the weakest members of the party is something like 8 hp, it's not game-breaking. And you can take it into account.
I don't want to have to derail my game for an underwater adventure just because the warforged tripped and fell off the rig, nor do I care to fudge the tactics of the enemy and have them not try the smartest tactic for the situation.
A recently referenced an excellent Dungeon adventure, "Steel Shadows," that focuses on warforged. Much of the feel of this adventure deals with the prejudices that people in the campaign world have towards warforged. This is a running theme in Eberron (some of the other races have to deal with it, especially changelings and shifters).
And here's my other problem: they hog the spotlight. To a certain extent it's expected, but where's the adventure that focueses on the prejudices that people in the campaign world have to gnomes? Or goblins? Or flumphs?
Nope, it's warforged, because golem-men are the new pink.
