By the way, free will existed long before Crowley tempted Eve to eat the Apple of Knowledge. The very fact that Eve gave in and ate the apple is an act of free will in its purest form. The same goes for Adam, who also chose to eat it. And the same goes for Aziraphale, who - may I remind you - is an angel who never ate from the Tree of Knowledge and isn't even human, yet still chose to give the flaming sword to humanity despite knowing it was against the rules. The same goes for Crowley, who asked questions and, by ending up in the wrong crowd, fell.
That means God built free will into all of Her creations from the very beginning. If that weren't true, the angels could never have Fallen. If that weren't true, Aziraphale would never have given away his sword. If that weren't true, humanity would never have been able to give in to Crowley's temptation.
"Well, you tempt them into that."
"Yes, but they can say no. It's the ineffable (free will) bit, isn't it?"
That's not an exact quote from the book, but yeah.
If everyone had been nothing more than puppets in God's hands from the very beginning, everything would have gone perfectly according to plan from the start. But every one of Her creations possesses free will - it was there from the beginning. Without it, none of what we saw throughout the book, or the first season, could have happened at all. Everything would have unfolded exactly as God wanted, without a single deviation.
P. S. Btw I don't think Crowley even realized he was giving humanity the knowledge of good and evil through that temptation. In Good Omens, it comes across as little more than a joke on his part. Sure, he was carrying out Hell's orders to stir up trouble in Eden and make Heaven's plans go sideways, but it never felt like he deliberately set out to grant humanity moral awareness. As I see it, he basically did it for the fun of causing a bit of chaos, without any conscious intention of giving humans the knowledge of good and evil.
"Would be funny, wouldn't it? If I did the good thing and you did the bad one".