I did neutral to get started.
I did True Pacifist to get the good ending.
I did Genocide for the challenge, not for the sake of killing them.
I did a Soulless Pacifist to make things right after that.
As long as you're the player you can make it up for them or **** it up. That's your choice. That's basically what the game tries to show you: as a player, you have unlimited power.
I may have killed them all but it was only once and I brought them back using the magic you call "reset".
that is not what the games tells, you have unlimited power but your actions will always have consequences, once you have done genocide you never get a truly pacifist ending, your soul is corrupted.
You bring them back but it still happened and you can't reset your conciencie
But, you can edit the files of the hame to make that statement false because, again, it's within the realm of possibilities as a player.
And either if you make a souless pacifist, flowey tells you **** is fine in there and that you shouldn't reset because everyone's happy. "But should you trust Flowey?" Yes. Why would he lie at this point? He became Asriel and made his mind back together. Flowey simply acts on self-interest, he's not actually evil.
Your actions have repercussions but that doesn't mean you can't do something about it.