They're really not.
First of all, no data is really lost with Git. Commits can be recovered from the reflog if they haven't been garbage collected, and there are ways of recovering anything on GitHub as well[1], even if it technically shouldn't be the case.
But this aside, data loss is circumstantial, like you say. I've heard the idea that force-pushing in general is harmful, when it's really not if you're working solo or on an isolated branch. Rebasing and force-pushing are just different tools in the toolbox.
In general, my objection is to the practice of describing any software as "dangerous". It creates an air of intimidation that prevents people from using the tools to their full extent, which when spread can popularize wrong practices among new users as well. This is why you see the person in the article claiming that they've always been a "merger", having a false dilemma between merging and rebasing, and describing their solution as "fearless". This line of thinking is also commonly associated with the command line and Linux itself, and is just harmful.
Instead, users should be educated on what the software does, which does require having comprehensive UIs and documentation, and designing the software with sane defaults, fail-safes, and ways to undo any action. Git doesn't do a great job at all of these, but overall it's not so bad either. What really hurts users is spreading the wrong kind of ideas, though.
