I don't understand why should String Theory be labeled as "scientific". Can you explain? Why cannot we be happy just calling it philosophy?
To me, "scientific" means "uses scientific method", which in turn is a set of tools that are pretty successful in understanding universe. Scientific method is certainly not fixed set of tools - for example, computer simulation became very useful only recently.
Maybe doing whatever string theorists are doing will become useful in the future, and as such their method will become part of scientific method; but since we aren't really sure if string theory itself is true, we can't consider their methodology to be useful (or useless) and so part of scientific method.
For me looking into String Theory's status as scientific/not-scientific is a good way to learn that the Popperian view of falsifiable==scientific is a bit too simplistsic and that classifying things as scientific/not-scientific may not even be a productive activity. It's just not that simple.
A good quote from that thread which may answer your question: "Anyways, my point is that String Theory is not just some whacky idea "what if everything was strings" that exists in a vacuum, but is rather a very natural and conservative extension of Quantum Field Theory to a more general and less arbitrary framework."
To me, "scientific" means "uses scientific method", which in turn is a set of tools that are pretty successful in understanding universe. Scientific method is certainly not fixed set of tools - for example, computer simulation became very useful only recently.
Maybe doing whatever string theorists are doing will become useful in the future, and as such their method will become part of scientific method; but since we aren't really sure if string theory itself is true, we can't consider their methodology to be useful (or useless) and so part of scientific method.