Mark 16:16 doesn't mention repentance. Do you think that negates the need for it.
1 Peter 3:21: The like figure whereunto even baptism doth also now save us (not the putting away of the filth of the flesh, but the answer of a good conscience toward God,) by the resurrection of Jesus Christ.
Baptism alone doesn't save us but if you don't put all scriptures together in context I suppose one could use
1 Peter 3:21 out of context to say the only thing neccessary for salvation is repentance.