it scans the original, destroying it in the process
So, regardless of any (multiple?) duplicates that might be sent where ever, you believe that the transporter is basically a suicide booth, for want of a better term?
Given the Federations high moral and ethical philosophy, I just can't see them allowing their people to step into such a machine, cargo sure, but not people.
If the transporter scans you and then sends a copy to the destination, why not at that point don't you (the original Butters) simply step back off of the platform and go about your day?
If you Butters believe that your presents on the platform was solely for the purpose of making a detailed scan for an eventual copy, where does the necessity of you death become a requirement?
how can you see without eyes and optic nerves
I guess the most straight forward explanation is that when you're transformed from physical to energy (a energy state) that you continue to have a "intact" energy body, you are for a fraction of a second an energy being, with operational eyes and optical nerves. Obviously Barclay retained his consciousness, so he also possessed a functioning brain throughout the transport process.