I'm not sure why people are against being able to have each job have its own myth cap.
It's not that people are against it, it's that SE have said it won't be happening and have given pretty valid reasons. It's actually not a discussion point anymore because we know what will be happening in 2.1:
- Myth cap will be raised to 450
- CT will provide another avenue for us to easily cap myth (and gear with iLvl 80)

The problem with an individual job myth cap is totally related to people staying relatively on par with each other. Apart from that it's also counter intuitive to the armory system. Apart from that there's actually no reason to be gearing more than 2 jobs to the teeth with ilvl 90 at the moment, apart from e-peen and burning yourself out of content.