To add yet more reasoning.
This forum thread is for example about adding the electrum appimage, which is a binary planned to be added to a Whonix “source package” which then would be compiled into a binary deb package.
The ideological issue here is, that it is not compiled from source during the process for creation of a binary deb package. (Which is difficult and could even have security issues unfortunately due to unverified third party library downloads.)
Electrum is fully Freedom Software. Electrum is not available as an up-to-date deb package from any source at time of writing.
On the other hand, it is the same quantity of “bad” as using binary Debian packages during build of Whonix. All of Tails, Qubes, Whonix and many derivatives does download binary deb packages from packages.debian.org during their iso/ova build process. Electrum is just another source of binary Freedom Software similar to packages.debian.org.