Theyre fanboys because they are defending the fact that a feature is missing from a game and twisting a negative into a positive.

So it is not just a matter of opinion, your position is absolutely correct, and no reasonable person could possibly disagree. The mere act of disagreeing proves a person unreasonable, or a liar, obviously motivated to come up with some desperate excuses because they are a fanboy.

So why was it that Larian, with complete control over the game design, somehow failed to implement this essential feature? I think there are a few more of those desperate excuses if you read the introduction in the manual...

It doesnt have anything to do with disagreeing with me.

Must be nice that your preferred playstyle matches up so well with the universal perfect truth of RPG game design.

A measured analysis of this situation would make a normal person wonder why Larian didnt include an option for respawn so that both playstyles could accommodated.

Perhaps they don't like respaning opponents? Maybe they didn't want to make a Diablo clone?
There are a lot of options they could have included, but didn't. Why not add an option for party members, with lots of interaction and personal history/quests, etc, for people who prefer to play party based games? Or is it ridiculous to compare a feature to a universal gaming truth such as respawning?

Instead people just say "its fine you arent a real RPG fan". Thats being a fanboy.

Nobody is arguing you can't like the style of games that you like, or that that isn't a perfectly valid position. It is not the only valid position, however.

Why would killing opponents be something you would want to avoid?

It can be very boring and repetitive, IMO, when you have to keep doing it over and over.
I have played games with respaning opponents, or random encounters, and have taken advantage of that to level when I've had trouble, or to get enough gold for new equipment, etc. However, the games in question were designed with that dynamic from the start. Sometimes there was enough to the game that respawning didn't bother me, sometimes I had to take breaks from the hack and slash, and a couple times I've just become too bored with it to continue. It is not up to the game to conform to my expectations, though.

How does having to clear an area again deny your sense of accomplishment for clearing it the first time?

By making it completely pointless.

Wouldnt that just mean your are satisfied with having cleared it twice? Double the satisfaction.

Doing pointless things over and over for diminishing rewards isn't my idea of unlimited satisfaction.

How does having to kill some enemies again equate to not having any effect on the game world? Thats an overreaction.

By definition, if you do something, and some short time later everything is back where it started, you had no effect. You have a little extra experience and loot, but the world itself is unchanged.

Enough is enough when I say its enough. Not when some developer says its enough. I want to be able to level as much as i please and then decide on my own that its time to finish the game.

Are there any games that meet that criteria? Even MMOs designed to be played for years have level caps. I don't know of any game that uses levels without at least a technical level cap.

Capping the number of available enemies in the game is tantamount to controlling how long players can play.

You can play as long as you wish. There is some a practical limit on how long any particular instance of the game can be played, but that is true of almost every game. RPGs as a group tend to have the longest playtime, but I think very few would meet your infinite playtime requirement.