Considering that the clones are being brought into a potentially low quality of life and don't have a choice in the matter, the priority should be with them and not the scientist because he "feels lonely".
But according to the thread starter:
*for the sake of the thought experiment we shall assume that the clones are grown in a loving, supporting and adequate environment to meet their needs
In your case, did you chose to be born?
The extreme pains I'm talking about are things like a fatal/near fatal wound, feeling suicidal, getting a part of me chopped off. I've never felt any of this, but anyone alive can potentially feel this suffering and if you intentionally create life you'd have to be prepared to take the feeling of guilt since they wouldn't be suffering if their consciousness never existed in the first place.
Don't you think these extreme pains are part of life?
What do you mean when you say: "to be prepared to take the feeling of guilt?"
Did you ask this question to your parents? Do you think they feel guilty when they gave birth to you?
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These clones, in their own way, because they are sentient, will feel pain; but at the same time, they will feel joy and happiness.