I still don’t get the rationale. It’s not like calibre somehow converts your ebooks to a proprietary format that you can’t use without calibre or that it modifies your ereader so that it won’t work without caliber either.
It's an ebook management tool. True, it's not proprietary, but if you rely heavily on it, it's a pain to switch to something else later. When you have very reasonable doubts about the future of the project, it makes sense to look for alternatives.
I don't think any good alternatives exist, but if they did, I'd probably switch in a heartbeat. The lead developer for Calibre is extremely annoying. RMS is easier to deal with.
I for one don't really deal with Calibre's author personally. I enjoy Calibre very much, and I'm grateful to its author. But you do you, if that precludes you from using Calibre that's fine.
I enjoy Calibre a lot as well and do not deal with him personally, and am grateful for what he has produced, but if there were alternatives that served my needs, I'd switch. Gratefulness doesn't mean overlooking one's flaws or loyalty.
Most of the time as a user you deal with the consequences of the developers competence or lack thereof not their personality. I'd infinitely rather use the work of a competent asshole than an incompetent saint. I've filled out bug reports and feature requests for calibre and found that even when I didn't agree with Kovid he was relatively easy to approach and responsive to dialog even when I didn't necessary agree with the response I feel like I've derived a ton of value from his work for zero dollars and zero cents.
I don't think any good alternatives exist, but if they did, I'd probably switch in a heartbeat. The lead developer for Calibre is extremely annoying. RMS is easier to deal with.