For the auto-commence, they'd have to have some way to automatically change you to the correct class/job, which might get tricky if you've got multiple gear sets for that job.

There's also the issue of someone going on unexpected extended AFK with this running (or just being a jerk). So they auto-accept, and some unsuspecting party is stuck with them AFK until they can waste a kick. Granted, jerks do that now, but at least now they have to sit there long enough to hit Commence.

And yeah, if you give people the option to not run with newbies, newbies are going to get screwed so hard. Yes, some people will start out still running with newbies, but building frustration is going to diminish that more and more; a lot of people are cool with newbies in small to medium doses, but would start opting out after being the only experienced player several times. Which just tilts the ratio that much more for the ones who're left, and so on.