Because, in making it go away it's being taken away from other players who do enjoy using the system. And usually it's about making other classes go away because they don't like them. That's why it can be considered inflammatory by some.
Another suggestion to is to try other kinds of systems before trying to change it to suit your preference, but the first thought is to make it go away so that nobody else can enjoy it?
Misery loves company and will always try to ruin other people's fun. That's what's wrong with this kind of thread. Let people have their fun and stop trying to change things in order to stop people from having their fun. And usually what happens to that person who wants to change things? They get told to go away.
How does suggesting replacing Vancian casting with an alternative magic system "take away your fun"? You can house rule it back in to any D&D style system you choose--just as we've been told we can house rule it out.
But apparently a portion of those who like Vancian magic are of the opinion that those of us who don't like it should be the ones to do all the house ruling and conversion work. Fair enough, I suppose, just be careful when you start claiming we're "taking away your fun." The door swings both ways.
Personally I'm rather surprised at the number of people defending it. Yeah, functionally it works relatively well. And yes, I realize that any magic system mechanic is in large part going to be a massive case of "suspension of disbelief." But it doesn't change the fact that in my opinion, it's the least "organic" feeling magic system out there. Meaning, if you were to create a mechanical representation of how magic works, it's by far the one I'd be least likely to "imagine up" in my own head.
Does that mean it has no merit at all? No. It's at least mechanically consistent, and certainly has lasted through 30 years of D&D gameplay, but I'm fairly certain that there are other systems, if implemented into the D&D experience from the ground up, that could be just as consistent, more fun, and make the in-game decisions more interesting and compelling than flipping through the books looking for just the right spell, and the perfect meta-magic feat chain to go with it.
I'm just not sure why that sentiment is offensive.