Board Thread:Legitimate Canon Questions/@comment-125.62.109.77-20150308124318/@comment-4091815-20150308155122

As far as we know, he wasn't talking about "just biting" Scott. It was more a "I brought you in to this world and I can send you out of it" threat one might hear from their Father.

His statement to Jennifer in 3(b) was bravado. In his own mind he is still the Alpha and always was. In reality Peter is a beta/omega.

Peter's reasons for wanting to kill Scott are his own but we can glean a bit from his rant that became the Benefactor plan. Peter doesn't like what he sees as "weakness" within the supernatural community. He wanted to wipe out all supernaturals and start over. It's not a stretch to say that Peter sees Scott's unwillingness to kill as a weakness.