It is a game, isn't it? Games have mechanics. If it doesn't have mechanics, you're back on the playground playing cops and robbers yelling "I shot you!" "Nuh uh!" "Uh huh!"
What makes one amount of gamism better than others? Worse?
Many people enjoy realism in a world. It makes it easier to relate to, which makes it easier to accept the setting in-game, which means you're less likely to feel separated from your character, which means it's a lot easier to roleplay.
Mechanics are necessary, yes. When they interrupt realism too much, it often leads to people getting confused. In my opinion, it's best if a game focuses on one appeal or another (gamist versus realism), otherwise you have people questioning things in the system.
Full plate takes 4 minutes to don, and you need someone assisting you to do it, or it's considered to be donned hastily. It's not really a gamist issue, since if you were attacked while not wearing your armor, then 4 minutes it about as bad as 1 minute. From a realism standpoint, it makes a difference, which I believe was the intent.
Then players begin to ask questions based on that perception of realism. Why can I only do this special use of a skill or combat maneuver from this feat when I get the particular feat? Why can't I do it in general if I have the skill at a high enough bonus? Why does a ladder cost less than a 10 foot pole?
The designers, in an attempt at balance between the classes, placed a lot of understandable gamist restrictions on the game. Why does a masterwork dagger cost nearly as much as a masterwork greatsword? Because wealth is factored into character power in D&D. That's why the economy is so wrecked. That's why there's no real enforced mechanics in pricing of objects, magic items, houses, etc.
4th edition catered to the gamist crowd. When houseruling 3.5, I prefer to cater to realism crowd. This usually means bringing casters more in line with melee, rather than bringing melee up to casters. It's also why, in my campaign, I've completely reworked the Craft skill, and imposed an entirely new economic model, based on a variety of factors, from size of objects to hardness to DC.
Of course, my campaign got so heavily houseruled that while it is still d20 based, it's entirely different from D&D, and I've tried to cut as many ties to D&D as possible (no gods from D&D, new unique setting, some unique races, entirely new Racial traits on races [along with Societal traits, National traits, and Regional traits], entirely new planes (with none of the old planes), no classes, self-created point-buy system for special abilities, new magic system to capture magic in a unique and versatile way, etc.). With the above knowledge, you can safely assume that my personal stakes in D&D have dropped significantly.
What we're mainly seeing in this ongoing debate is people who want to bring spellcasters more in line with melee (in general to enhance realism in the world), and people who want to bring melee more in line with spellcasters (to enhance their game and make it more enjoyable, since roleplaying is not entirely dependent on realism). It seems clear cut enough to me.
