That is a total over-simplification
It is a waste of time and money for those who are not particularly academically minded; for those who are though, and who might wish to ensure they have a backup career of any kind at all, it is a very good idea, and with perseverance can produce great returns.
Lesson - don't bother going to a mediocre university without a plan - and always sign up to the UAS if you have even a partial interest in a mil career. Work your debt off in holidays, and remember that the student loan is a factor in reducing earnings (unless Scottish).
In pure financial terms, yes, it may raise your debt levels - it may however open far more doors to get into airlines. Best of all, it will lead to an open mind.
Don't close doors.