I see this kind of sentiment expressed very often, actually. Not universally by any means, but often enough that it would seem to be how many interpret it.
Broadly speaking, I prefer when the GM has designed scenarios without that sense of neutrality as is assumed with the old school modules and similar. Here's the Keep on the Borderlands, plug in party A or party B, and see how it goes. I prefer a GM who is thinking of party A when he designs the scenario.
This is what I have in mind when I'm talking about this. Although I can understand the appeal of a set scenario and seeing how different groups may handle it, and the shared experience that creates across the hobby....it's not generally something that any individual GM or group needs to worry about all that much.
I do find that many GMs that I've played with, and that I've chatted with here, seem to routinely eschew neutrality in this regard, as well as in other ways, such as fudging and curating experience and the like.
So, prior to answering this specifically, I am going to go a little "meta" here, because I don't want this to be misinterpreted.
One issue that I often have in these discussions, and I try to be mindful of, is that to many of these discussions end up as arguments. In others words, instead of looking at these conversations as areas where people can learn from each other (and find places of mutual agreement), it too often devolves into arguments about things- usually pretty stupid things.
A big part of is the nature of internet forums; you post on a public place. If someone agrees with what you say, most likely they do nothing, or maybe give you a reaction (a like, a laugh). So already, any feedback you get is most likely self-selected into people that want to argue or disagree with something.
I don't immunize myself from this either. Look, for example, at the response I gave to you; even though I almost entirely agreed with what you were saying, my response to you was about one area (and one sentence!) from a larger post that I happened to partially disagree with. And a lot of this back-and-forth ends up in frustration, if for no other reason than, while there are a few posters I just cannot abide, for the most part I think people confuse discussion with argument.
Now, with that background in mind, and with the hopeful understanding that I am not advocating for a particular position, but merely observing certain differences and discussing them ...
I think that if you read the pages in the DMG I referenced that the idea would be a little more clear, but at the most abstract level, I think that it is a truism that any good GM cares that her table is having a good time.
I just think that the GM who is approaching the game in the "neutral referee" manner believes that her table is going to have more fun if they use that method of adjudication. They will, of course, select scenarios (or create them) with the particular party in mind, but the choice of system itself is because the table is a fan of that system, and thinks that it will, overall, bring the most enjoyment.
That certainly doesn't mean that it's right for all, or most, tables! I would go so far as to say that this mode of GMing is definitely in the minority- but there are still some who enjoy playing that way.
That's why I think a lot of these conversations often get short-circuited; earlier, someone mentioned the "best practices" as opposed to the "one true way" issues that pop up. I think it's unfortunate, but what happens (IMO) is that discussions get short-circuited because they aren't granular enough.
For example, I think it would be possible to have a conversation about best practices and/or tips and techniques for a GM that is using "neutral referee" approach. Or for a GM that is using "fans of the players" approach. But instead of either, you end up having people argue about the two approaches (and others!) in comparison to each other.
Woah, that was very long-winded! Um, something something bards suck.