Why is Satan the 'evil one'?

Hello there! Asking this for some input. You can answer without reading the rest of this question if you want, but I do not recommend it.

Here we go:

In Genesis, Satan gives Adam and Eve the gift of knowledge of right and wrong by the way of the fruit from the tree. God sees this as "bad" or a "sin," and punishes Adam and Eve by taking away their immortality and kicking them out of the Garden they lived in. God could have forgiven them (I've heard from many christians that god is loving and forgiving,) and seen that they wouldn't have known not to eat from the tree in the first place, but he decides to basically kill them instead.

Also god hates knowledge apparently and sees it as a sin... interesting.

See the book of Job where Satan bets god that Job will curse him if his life is made miserable enough. God kills Job's children (NOT Satan,) and Job ends up not cursing god (even though god would have deserved it,) so Satan loses the bet.

As well, the book itself can't decide if Satan is tied up or free to roam the Earth:

[2 Peter 2:4]

For if God spared not the angels that sinned, but cast them down to hell, and delivered them into chains of darkness, to be reserved unto judgment.

in opposite, this verse here

Job 1:7

"Then Satan answered the LORD, and said, From going to and fro in the earth, and from walking up and down in it."

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All Satan seems to do in the bible is test god and his followers. There is no record of him killing anybody, torturing them, or sending a plague onto them.

Now, let's take a look at God's crimes:

God destroys all life on Earth in a great flood, except for a drunk (Noah) and his family, for failing to worship him.

God's tenth plague upon the Israelites was the unjustified murder of all firstborn sons in Egypt, which undoubtedly included little children.

Before sending the plagues to Egypt, God "hardened Pharaoh's heart" so that he wouldn't let the Israelites go, so he could have an excuse to visit horrible plagues upon them, like boils, killing cattle and murdering all firstborn sons. (Exodus 4:21)

God orders the Levites to kill their "every man and his neighbor" for worshiping another god. This cost 3000 lives. (Exodus 32:27)

God sends a plague to the Israelites, apparently feeling that mass-butchery wasn't enough of a punishment. (Exodus 32:35)

God kills Onan for refusing to impregnate his late brother's (whom God also slew) wife and instead "spilling his seed on the ground." (Genesis 38:8-10)

God kills the entire populations of Soddom and Gammorah (again, including women, children and infants) for practicing certain sexual techniques.

God kills over 50,000 people for looking at an ark. (1 Samuel 6:19)

God kills 70,000 people because King David decided to have a census. (1 Chronicles 21:7-14)

God approves of slavery, and instructs owners to beat their slaves. (Proverbs 29:19)

And, finally, God makes sure that if you are guilty of even the smallest transgression, you shall suffer endlessly for all eternity, following a dramatic homecoming for Jesus, who will be extremely ticked off at everyone for putting him to death, even though it was just the Romans and even though he knew what was going to happen beforehand, and he could have easily avoided it by using his power as God to perform a miracle and prove who he was.

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But okay... "this isn't the same god as the new testament! Old testament is wrong, and should be excluded!"

Okay then; there goes your entire story of Genesis... making god sending his son to die for our "sins" in the New Testament rather pointless. It also removes god taking away our immortality in Genesis, yet people still die in the rest of the book.

SO... How, why, is Satan the "evil one"? Tell me, and back it up with evidence, please.