The reduced carbon impact is one of the reasons to recycle, but your not the first person on HN that I've seen claim exactly the opposite.
(Of note, burning the trash and using the energy produced is also better for climate change than landfill).
But recycling plastic specifically uses less energy which in turn saves carbon.
Even burning the plastic as fuel is regularly cited by life cycle analyses as less carbon intensive than landfilling it and creating totally new plastic to replace it.
However, other factors include: labor; transportation & waste costs (glass is heavier and breaks easier); and labor-geographic efficiency enabled by lower transport costs—for example, you might choose fewer bottling plants farther apart for cost efficiency, so you can reduce overhead and concentrate your labor costs in cheap locations, rather than every town having a small bottling plant, or stores having fill-n-cap stations directly in them, or whatever.
[EDIT] that is, with lower transportation costs of plastic you might be able to concentrate production in places with cheaper labor.
That's certainly the case on a one plastic bottle to one glass bottle ratio, but I wonder just how energy efficient is making that bottle over the glass one? Twice? Ten times? A hundred? Then how many times will a glass bottle get reused on average? What sort of resources are used in the process of bringing them back and cleaning them?
This might be my bias as an Australian, tons of space but already having our natural wonder smashed by climate change, but I'm very uninterested in 'pro environment' moves that results in trading higher emissions for less land fill.
Although potentially an argument could be made that because ocean waste is less contained and more harmful than landfill, a 5-10% hike on plastic bottle drinks in low water polluting countries and using it to subsidise glass bottle drinks in high water polluting countries would be worthwhile.