Can you explain how "God meant it for good" somehow really means "God allowed it for good"?
Yes, I can.
In fact I already have, but I am a patient man.
The word "allow" has a definition of more than one will.
That part is important, and I need you to follow my logic—you have a predisposition not to see the logic here, so you need to follow this closely. The word "allow" has, by definition, the presence of more than one will. That part is very, very important.
Now, we have to ask ourselves, how many wills are in this passage? How many wills are described and illustrated by these words?
Now if someone "means" something, we speak of "intent." This "intent" is a desire, a purpose, a direction of the agent—that is, someone is "meaning" to do or accomplish something, they have a plan. For an agent to have a plan this requires a will, a decision maker, to pick among options and settle on one thing to "mean."
Rocks don't "mean" something. A tree doesn't "mean" to wreck your house, it just falls on it. Meteors don't "mean" to flash in the sky, they just do by rote physics with no intention. So to "mean" something logically necessitates a will.
Now how does "allow" interface with "mean"? Let's say, we are playing poker, and I go all in with a bad hand. Then you call me. Now I say, "I allowed that to happen—I wanted you to win." Perhaps, because you are a keen player, you "meant" to win by skill. And I "meant" to let you win. Now we have two wills "meaning" two different things.
Now suppose, you were a mean person, and you really wanted to rob me of all my money. But I am a kind person, and I wanted to let you have it, because you need to pay your rent and buy groceries, and you are a little down on your luck. Then I say, "You know what—you meant that for evil, but I meant it for good." There is two wills there, and two people meaning two different things.
Now suppose I uniterally decided to decree what happened to you, and decide your choice for you. That requires removing your "mean to," it requires removing your determination as an agency, and replacing it with mine. So now, whatever you do, is only and solely what I decide for it to be—there is only one "mean to," and that "mean to" is mine. I force you to call by hypnotizing you, for your own good.
Which of these descriptions is in the passage?
One "will" or two?
One "mean to" or two "mean tos"?
One "purpose" or two "purposes"?
And thus we see that the text is actually an excellent proof of libertarian free will, and completely disproves monergism.