But people have been shown to consistently underestimate how much they are going to change in the future.
The decision is being made for a person that is technically different from the current one. Deciding to kill someone who is not 100% you is by definition murder, not suicide.
This 2013 study.
Edit: how am I appealing belief? I mentioned a scientific study and made a simple connection. Am I assuming the science is widely believed yet unproven?