If you have no sin you have the right to cast the first stone
Why? What's the logic behind that? If you have no sin, you see the world as it truly is, namely flawed, corrupted, you see that no one acts badly from their own desires, but from corrupted desires, experiences and influences. We, the sinful, catch glimpses of these issues sometimes and are able to forgive others because we realize that their actions were heavily influenced by their experiential background. How much more would someone who sees the entire picture be able to understand this? And once you've understood that no one is truly guilty, you have no right to punish, no right to cast the first stone.
Why would God refuse the desires of someone who did not want to be with him?
I never said that. I said they would cease to exist. But even your option sounds more merciful. On a rational level, it truly is more merciful to force someone to be in a state of frustration within non-painful conditions for eternity than to force someone to be tortured in flames in a state of agony for existence. That's just a simple ontological truth.
How can you claim that a being with a pure heart would force people to spend an eternity in his presence if they clearly didn't want to?
Again, I did not claim that. I said that He would have designed the system in such a way that any creature who tried to sin would simply vanish away in a non-painful manner before being able to accomplish their sin. When Eve reached for the forbidden fruit, she would have simply vanished away into nonexistence.
But even if, hypothetically speaking, that wasn't possible and the entire human history had to happen, I think we can agree that if you were given the choice between having to spend the rest of your life being a house slave for, let's say, Hitler, having a place to live, good food, free from any type of harm or abuse,... and being tortured non-stop for the rest of your life, you would choose the former. It is my belief that any sane person would make that choice because it is ingrained in our human nature to avoid extreme suffering for long periods of time. Even spies who were tortured during war times had some sort of poison hidden in a tooth to avoid the torture.