That distinction is certainly a bit vaguer if time travel be involved.
The planet simply existed in the future.
Suppose a method to send information back to the past exist, and an observer thereby be allowed to gain information of his own descendants, and thus elects not to have children by influence of that information sent back in time, is that murder?
What if the information channel be full duplex, and the observer be allowed to converse with his own descendants, and based on that decides to not have children?
The way I see it, visiting the planet that exists in the future from one's own frame of reference is nothing more than such a full duplex information channel.
Of course, the hypothetical existence of such channels offers more problems, which is probably why they don't exist outside of fiction.