Sometimes people minify js to make better usage of the network, not because they want to hide from you the js source code to gain more power over you as a user. There's no practical way to run your specific modified version of js in a browser to customize your own site experience because the js code is just a tailor made client for the site's server code.
Look this way: They could have rendered the whole html that you see in the server side, and still there are tons of websites that do that. and in that case you would have just the bare html and css in your hands, which doesn't change the fact that you are using non-free software that generates that html; still you wouldn't have a problem with that because "you're not running non-free js code on your browser".
but instead they chose to split the software: they hand it to your browser a piece of the software in js so that you can have a more dynamic experience. As a plus your browser doesn't have to call the server all the time to generate an updated DOM. Now UI logic can be very hard and complex so instead of handing you a plain js file which can be many KBs long, they minify it, and maybe gzip it so they can better use the network resources, potentially saving energy for the benefit off all mankind.
I see this way: It's just a website, but now some of the server's code is offloaded to the browser by means of js. But it is still a website.
I don't think it is reasonable asking every website to stop minifying the js and to provide a way to submit a custom modified form of js client code that interacts with the website in a customized way. That would require to also release the server code, which would mean that to be free all websites that deliver js client code to web browsers would have to release their server code.
Can you all see the problem here? js client code is not the same thing as regular installed on my pc software.
I have to trust my libre browser, which is in fact installed on my local computer and which I can modify and inspect the source code. I trust that it is written in a way that stops client js code from doing harm to my privacy and freedom.
We have different classes of software here. Software fully installed locally on my machine is one class of software. Server software, which is not running on my machine is a different kind of software. And software that is split between server software and client software *running in a libre sandboxed environment installed on my machine* is another class of software entirely.
I would assert that each class of software described above brings about different philosophical and ethical questions and deserve to be differently treated.
For starters, I would argue that a js client code, *running on my libre sandboxed browser environment*, which is really just a part of a much larger software, which is a website, does not harm my freedom and my privacy as long as the libre browser is properly constructed to properly handle js client code.
Doesn't this proposition seem reasonable to you gentleman?