Are you going to go the bullshit route of "they aren't true Christians"?
If they deny the deity of Jesus Christ, then yes.
So you're past the whole must think the Bible is inerrant thing, okay. Well, there are Christian who deny the deity of Jesus, too. And you don't get to decide who is and is not a Christian.
If a talking snake is a problem for you, then how do you get over a deity in a man's body, dying and remaining dead for 3 days, then returning back to life and walking and talking with people for 40 days?
God did it.
The snake was just a mythical creature in a fairy tale, obviously. It doesn't say that God had anything to do with it talking, unlike the resurrection.
Genesis 6:6 doesn't show a mistake, merely that God is an emotional Being and He is expressing His grief over our continued sin. Since morality, right and wrong and emotions are all constructs of His, it is perfectly consistent for Him to express His sorrow this way.
It says he regretted. That's a mistake. Your just making up stuff to aviod admitting your error.
Then you would need to show that He meant it as some sort of allegory. All of the text suggests that it is to be taken literally (unlike Revelation).
It has a talking snake and magic fruit and it describes a series of events that we know could not have happened. It was a just-so story that the jews told around campfires. It
screams "not-a-true-story".
But I'm sure you'll just dig your heels in and make up some more crap so you can maintain what you already believe.