If you've never studied magma then why do you think you can make assumptions about it 
In the same spirit then i challenge you if you've never seen the earth is flat how can you make assumptions about it? (your eye isnt sensitive enough and no ones presented any real evidence on here)
I believe science is as much about what we can see as what we cant, geology is an observational science still to this day, many of the processes the earth undergoes we cannot recreate in a lab and thats what makes it so dahm interesting. Instead of seeing the process we often only see the result or part of a much larger system in action all earth sciences will extrapolate the information they observe to come to conclusions that fit with other widely accepted theories. The FE theory isn't conclusive, it doesn't make any logical sense with the scientific knowledge of the day.
Science is progressive, once every one believed in a FE type model but time, evidence and research has proven the model flawed and so the consensus is replaced with a more robust model, that is true science. To deny such processes as plate tectonics is madness as its a corner stone of the earth sciences, when it has been subject to 1000's of reviews and research pieces.