Emulation. Let's talk about it. Good? Bad? Ethical? Unethical? Well this is my opinion. Emulation is important. It allows us to preserve games for the future. Some of the media games are on, such as discs, are threatening to deteriorate after time. That's first and foremost before you answer any other questions about it.
Is it good? Well yes. I believe so. As stated, it's the best way to preserve video games. It's also a good way to introduce people to retrogaming without the need for expensive original hardware. There's also ethical ways to emulate games- such as the NES games and SNES games offered with a Nintendo Switch Online subscription- without resorting to computer emulators and downloading roms.
Is it Ethical? Well it depends. As stated, many companies are starting to offer back catalog games or arcade games for sale or access. This would be ethical and paying the company for it's work. Of course, downloading roms from the internet to play on an emulator would be less so. Even older games may still be copyrighted by existing companies, while some games may no longer have a copyright holder.
Games without a copyright holder are generally considered 'abandoned' by many folks and 'okay' to emulate compared to say, games owned by say a company such as SEGA.
In the end, my original, stated opinion still stands. Emulation is important to the preservation of games.