"....we have better think...." 'Have' here should be 'had' Other than that this looks really good.

The previous answers have each corrected one of the two errors. If you combine Wesley and Misa's suggestions, you'll get a correct sentence. As Wesley pointed out, it should be "had better" (not "have"). (We) "had better" is a fixed phrase which never changes. You may hear some native speakers say "We better", but this is not 'proper English', so to speak. You could get away with saying "we better" in casual speech, but it is not acceptable in writing. As Misa pointed out, "rethink" takes a direct object, so you need to remove the preposition "about" : we rethink something. Apart from those two issues, it's well written and sounds natural.

It should be "then we better rethink the concept of what makes us human." The rest looks good.