[Jweb_Guru]

If you don't consider measurement ontologically special, then you need to somehow derive a physically meaningful Born rule without reference to measurement, which so far is something that AFAIK has only been accomplished in theories with large amounts of nonlocality and extra assumptions. The idea that people cling to the obviously false projection postulate out of obstinance is really strange to me, there just aren't very good alternatives available (at least not with the math fully worked out).

[konschubert]

I would love to consider measurement something ontologically special, but it's not possible because there is no well-defined definition for what a measurement is.

The definitions I have found always invoke the presence of a "classical system"/"observer".

But that just kicks the can down the road, because there is no well-defined definition of a "classical system" either.

[Jweb_Guru]

Sure. Everyone agrees Copenhagen is just kicking the can down the road. I'm just saying, let's not act like we have a ton of viable theories to fill out the rest of the road; in the meanwhile, we still have to perform measurements and make predictions, and the projection postulate is handy for that.

(It would help tremendously if we ever measured quantum states that weren't "collapsed", but as we've never done this so far it makes most of the stochastic collapse stuff hard to justify, even if it seems intuitively like the right approach).