Ah, if you took that as me taking a stance on justification in general in all its cases, then once again: I'm talking about how it applies to notes in Joplin. Sure, make the leaflet for your lawyer's office more formal this way, why not. That's not the case I'm concerned about here.
Thanks for the links. They seem to mostly say the same things mine did, though. Some random outtakes:
[Fully-Justified Text] May require extra attention to word and character spacing and hyphenation to avoid unsightly rivers of white space running through the text.
Generally, typeset left-aligned is easier to work with (i.e., requires less time, attention, and tweaking from the designer to make it look good).
There is no right or wrong way to align text. Use the alignment that makes the most sense for the design and that effectively communicates your message.
My opinion: right rag is the right default for Joplin.
Although some designers will tell you different, there’s nothing intrinsically wrong with justified text, on the web or otherwise. But there’s a lot wrong with poor justification, which is all the web platform has been able to manage.
I'm not sure if you've read the link to Cutting Edge PR you've posted, but that one talks about how justification can maybe improve things "in narrow columns". Also quote:
The above results are quite clear: typesetting justified on left and right clearly works best for good reader comprehension of columns of text in printed publications.
Again, that is the case where someone doing DTP makes sure the text looks good. It also seems to talk about multi-column layout. Neither of those are what the notes in Joplin use, so that article seems irrelevant.
What seems surprising to me is that not only there are studies that study that (and they find justified text hurts legibility, especially for dyslexic or vision-impaired people) - even one of the articles you have linked - this one - spends about a third of its text talking about exactly the issues it causes. 
Anyway, interesting discussion - I've read some interesting articles while googling for details. Fun times.