This is a bullshit argument that never gets applied to any other live language. The characters are different, people who actually use them in daily life recognise them as conveying different things. If a thumbs up with a different skin tone is a different character then a different pattern of lines is definitely a different character.
The underlying implementation mechanism is not the issue. If unicode had actual support for Japanese characters so that when one e.g. converted text from Shift-JIS (in the default, supported way) one could be confident that one's characters would not change into different characters, I wouldn't be complaining, whether the implementation mechanism involved variant selectors or otherwise.
