Point taken about the elves, but that in no way hurts the argument because of the aforementioned "not a lot of obstacles in the core rules exist that they have immunity to; a lot of obstacles in the core rules exist that the warforged have immunity to" case. The Warforged are a much grosser offender in quality and quanity than even the elf.
I'm thinking that "different is bad" isn't a very strong argument.
Oh but it is! A DM of basic skill level has it within his power to run a fun adventure for a great wyrm red dragon, a stone golem, an ice elemental half-vamire rogue, a dwarven wizard, a human paladin, and an intelligent gelatinous cube who has the ability to cast cleric spells
somehow. Most DM's are perfectly *able* to run an adventure with these characters, and do it in a way that's fun and richly engaging for all involved. Hell, I half expect someone who reads this post to go out and do just that.

Balance and power are all ultimately campaign-specific ANYWAY.
But most DM's don't really want to be bothered with taking into account all those dramatic differences in the party, and if they do it once, they generally don't want to have it as repeat themes in their ongoing game. It's just not fun for most DM's to constantly keep in mind the wild and wacky powers of this kind of party, while still introducing challenges where the paladin and wizard can feel useful. Or at least, if this point was wrong, I imagine I'd be reading less about humans and halflings on these boards and more about wraiths and dragons. The Core Rules keep everything humanoid for a reason, after all. And the game is set up with that in mind. The Warforged break this sucker wide open.
You have, on a drastically smaller scale, the same thing. They don't work like the other races in the game. Some DM's (such as myself) don't really want to be bothered with taking into account the dramatic difference of this ONE character, or this ONE race. From a design standpoint, on this note, the are a
failure for some in a way that could have been avoided while retaining their unique flavor and fun concept with a few simple adjustements. As far as I can tell, the designers noted that there was this easier way to do it, but decided not to go with it because they felt the warforged should feel totally different but still be basically playable. They succeeded on this goal, but I think it was the wrong goal. I don't know why the warforged deserve to be drastically different. And I certainly don't want them muscling in and making me accomodate their difference just because they have a cool idea attatched to wonky mechanics.
In a game where all the players are supposed to be "separate but equal", at least in terms of overcoming challenges, a dramatic difference of any one feature is, in effect, an inequality. The warforged are not equal to any other race. This difference is bad for MANY reasons, but most importantly for me, it's bad because I have to spend a few minutes thinking about what the Warforged character could do because he's a Warforged in a way I don't have to think about what the halfling can do because he's a halfling. Elves do share that thought-hogging process, but when it's three spells in the game or one attack from one monster, that's not a major time-consumer. The broad, sweeping immunities and non-living-ness of the Warforged, however, ARE.
Different is bad. Different requires special thought, special consideration, special preparation, special attention. They hog the spotlight and demand to be paid attention to because they're so dramatically different.
For comparison:
* Elves are immune to Sleep, Deep Slumber, Dream, and Nightmare spells, and to a ghoul's paralysis. If I have an elf in the party, I should be taking these into account. Annoying, but not that big of a list.
* Warforged are immune to all those. Furthermore, they are immune bleeding, starvation and thirst, suffocation, disease, nausea, sickness, normal fatigue and exhaustion, and drowning; alter self (and the various spells built off of it) can turn them into golems; they are immune to charm person, hold person, hold monster, poison (the spell), touch of fatigue, ghoul touch (the spell), ray of exhaustion, reduce person, contagion, enervation, mass reduce person, waves of fatigue, dominate person, part of the eyebite spell, flesh to stone, mass hold person, waves of exhaustion, mass hold monster, and energy drain; they are immune to a defining or prominent damage form from any creature using poison on a weapon, especially if said weapon only deals damage to deliver the poison (daggers, blowdarts, shuriken...); they are immune to a defining or prominent damage form from aranea, athaches, basilisks, beholders, belkers, carrion crawlers, chuuls, cloakers, cockatrices, bebeliths, hezrous, quasits, succubi, bone devils, imps, devourers, dire rats, doppelgangers (since they can't mimic a warforged), driders, drow, ettercaps, formian warriors, formian myrmarchs, violet fungus, gorgons, homunculus, all lycanthropes (especially wererats), medusa, mohrgs, mummies, all nagas, night hags, night crawlers, otyughs, phase spiders, pseudodragons, rasts, red slaad (one would think a robot body can't incubate eggs...), blue slaad, spectres, spider eaters, stirges (debatably; it's said they suck blood, so one would think a robot wouldn't be a target), all swarms to a certain degree, but especially bat, centipede, hellwasp, rat, and spider swarms, troglodytes, wights, wyvrens, most yuan-ti, all vipers, giant bees, giant wasps, all monstrous centipedes, all monstrous scorpions, all monstrous spiders, and probably a few more that I missed. If I have a Warforged in the party, I should be taking these all into account. This is not acceptable to me. That's a BIG part of the game that the warforged just waltz through.
It was acceptable to the designers because they figured there were other ways to challenge the character, and that these still pose a challenge for the party as an entire unit. But if the major story arc involves yuan-ti and a nest of spiders and drow, well...the Warforged character will probably feel especially powerful when compared to all these guys who have to keep saving. Or if it involves a necromancer-king with an army of basilisks and spectres at his beck and call, the Warforged will again feel mighty indeed, in compairison to others. Stirges used to spend the rescources of the entire party. Now, one guy is immune. All characters used to fear getting inhaled by a Belker. Now, one member doesn't. Mummies and lycanthropes struck terror into the PC's because they could die or loose humanity from a powerful supernatural disease. Now at least one character doesn't have to fear that.
In exchange, he can fear rust monsters and well-prepared druids.
Yeah, this seems totally on par....
