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You did want IS in the zoom so you do understand the need for IS at short focal lenghts.
You are concerned about cost, so you understand that a prime is cheaper than a zoom. The IS mechanism in the prime will also be smaller and cheaper than in a zoom.
This gives me IS at short focal lengths at a low weight and cost, and probably with better IQ than a zoom. What is wrong with that?
You miss the point - an f/1.x zoom is highly impractical so you need an f/2.8 with IS to compensate. If your shooting style - such as weddings requires flexibility then primes are a problem. Since you can get an f/1.4 24, 35, and 50 - a 28/2.8IS is redundant. It will be cheaper than the 1.4L, but not by a whole lot.