Neonchameleon
Legend
1- Are you absolutely sure it is the best for everyone that a Cleric (who starts off as an inferior melee warrior that the fighter classes) buffs himself and become the best melee warrior of the party? Or does this mean you end up with the Cleric stepping on the Fighter's melee role, and having 2 good melee instead of having one decent (non-buffed Cleric) and one excellent (buffed Fighter)? Couldn't it be instead better to buff the best guy (Fighter) to excellent damage output and AC so that he can really be the 1st line of defense, and the Cleric is free to do more things?
That depends. The problem with this case is that the cleric not only steps on the fighter's melee role, he also covers his own. Which leaves the fighter wondering why he wasn't playing a cleric. And it's not a bad option for the rest of the party (other than the fighter - and even then the cleric's taking hits for the fighter). If the cleric wants to behave like a knight in shining armour this is a strong and slightly selfish choice, but not really overwhelming. (Druids are another story - getting two people for the price of one).
2- Are you absolute sure it is the best for everyone that the Wizard becomes nearly-untouchable after self-buffing with protections from everything, when anyway she's still going to stay as far as possible from melee, when everybody else is dying on the front line due to low defenses?
If the wizard was just untouchable, no one would care. The wizard tradeoff is that the wizard has the best offence in the game but is a glass cannon that other people have to protect. Being nearly untouchable frees up the rest of the party. But it's not the untouchability of the wizard that's the problem. It's making the enemy irrelevant. It's the debuffs that are the problem. An untouchable wizard plinking away with a crossbow wouldn't worry anyone. (And don't suggest SR to stop debuffs - there are plenty such as glitterdust, solid fog, or black tentacles that ignore SR or even magic immunity). But even with the debuffs the wizard would have weaknesses - being squishy. So would be a drag on as well as a boon to the party. That's what the buffs prevent.
Wouldn't it spoil the game if the Cleric would only heal himself?
I'm going to say no - you can be a perfectly effective cleric in 3.X and not actually heal anyone except through a wand of CLW. Just make sure everyone knows you aren't playing a healer. There is nothing inherently wrong with wanting to play a Manifestation of Divine Wrath. (In 4e it's called the Invoker - but the 3e Cleric has it covered). It would spoil the game if the Cleric signed up to be a healer and then didn't. But that's a different story.
So why should it be different for buffing?
It isn't. As long as people are helping the party I don't care how. And a buffing tank is helping the party by being a tank. I don't honestly care if they have "fighter", "paladin", or even "cleric" or "druid" written on their character sheet if they can do what they signed up to. (And given that across the day clerics and druids have the most hp to play with, and that clerics get all the armour proficiencies then the only thing they lack for tanking is the weapon mastery - they can provide their own teeth when they want to).