Anyone can choose to install whatever software they choose on their device, but the "free" in free software specifically refers to the freedom to read and modify the source code.

Under the philosophy of the FOSS movement, all proprietary software are by definition unethical.

Since Lemmy and the larger fediverse is the choice for many free software advocates, it's natural that you see this kind of backlash when fundamentally unethical software to interact with it is released.