Please don’t theme our apps

>If it's a bug in the theme, the application developer is just not responsible for it.

And how many times would they have to tell the end user who opened an issue on their app's tracker that?

The situation is even more tricky as what is being modified is not even the software itself but the system dependencies. Essentially the developers in this letter say: do not run our software on an environment that is not the one we support (in practice fedora or a close clone of it) and if you create a distro make sure its a clone of what we support.

I understand the fact that developers do not want to support bugs due to user modifications and strange environments. Free software doesn't imply free support so they can put any restriction on what they want to do. The letter however would have been much less weird if it said "we cannot ensure quality of software X except on our build running on a supported environment, if you run the software elsewhere or with changes (and theming is a change) please don't call it X to avoid confusion and remember you are on your own".

What Firefox did I think its a smart solution to this problem. " We offer Firefox on platform x,y,z. If you build it on something else, call it something else, if you run it on another platform remember you're on your own".

The author presents valid and sensible issues with the state of theming on the GNOME platform. And the overarching topic is essentially User Experience.

Even the slightest change in color can introduce friction between UI elements. Or to be more extreme, if a theme turns your entire app into a white blurry mess, you would get mad at the application, and not the theme. Although many of the same design principles are used in the making of either a chair or a graphical user interface, they are definitely not the same in any regard.

On the topic of icons: just like language, they evolve over time. On top of that, icons can have different meaning depending on your background. Icons can be combined to form a composite icon, and now imagine one of those icons is not displayed as you intended it to be. The entire meaning can change because the design intentions are lost.

On the topic of branding: it's not about your desktop being a billboard. It's about being able to recognize the brand across different operating systems, and it's also - more or less - the only thing about the product that is not designed for the purpose of user experience (but in a sense, they still are). And let's be honest: most apps we use in our day to day life have very tame brands and adhere to certain standards. That is because the apps we use are usually good, and we throw the bad, obnoxious ones away really quickly.

All in all, the author presents valid concerns, especially if you don't project them on how you prefer your UI, but rather, how potential Linux / GNOME users could have additional difficulties because of theming issues.

And honestly, complaining about the harm to your brand, come on. Give me a break.