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."
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.
In the meantime it's generally best to listen to scientists talk about it to get a feel for its standing: https://www.reddit.com/r/askscience/comments/28pzc1/string_t...
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."
And here's a blog post (series of posts) linked from that discussion which may also help: http://profmattstrassler.com/2013/09/23/quantum-field-theory...