One good reason why you'd want to use 2 for learning is that any job would be using 2. 95%+ percentile chance. It's not worth debating you on this if you don't work in Python for your day job. There's just so many misconceptions in what you've said.
From the way it sounds, you don't, and Python3 is hardly a dialect. The challenges of Python3 aren't for me or you, it's for library maintainers. And anyone with years of software built on 2.x (which is nearly all of us). I assure you moving from 2 to 3 as an end user is not a challenge. I have used Python3, since 3.0. It's no different 'dialect'- but when I last did (3.4), I found major performance regressions in basic functionality (JSON processing) and I think most of us have given up on Python3 (there are plenty of reasons). I'll revisit the idea of moving to it in another 5 years.
These issues are going unchecked in Python3 because there are no users. This is a major problem and plowing forward with Py3's development is a huge mistake. It remains to be seen what the consequences of this are.
It's simply propaganda to insist everyone is taught on Python3 as if it's the future of the language. You know it is a logical fallacy to appeal to authority. Python.org is taking a political stance, not one based on the real world. Python 2.x is the present. If you don't think so and refer to Python.org you're not programming in Python for a living. There's a major disconnect between the majority of the users of Python, and the core dev team that run that website. No one knows what the future of Python is yet, TBH Python.org should not be presenting 3 that way. In reality it's the experimental branch.
If you are using Python, then use 3 if you wish. Trust me, no one cares. You won't have support from most major distros and no online hosts. Google App Engine, Azure, etc are all on 2.x. You can't be doing too much though to not be running into missing libraries and roadblocks.
The silent majority will move to 3 if and when it ever makes sense. More likely we'll either go with the a fork, or simply move onto another language for the type of work that we do. Porting/testing is very expensive, why bother with that for no gains? We'll simply move to something else and the majority of the userbase will be gone.
There's only gains by using 2 but think what you will. Everyone is free to use what you want, including schools. I'm just explaining why it's not as simple and straight forward as you put it.
If it were that easy, there wouldn't be any controversy.