1. I don't have to 'believe in evolution'. It is a proven, scientific fact(despite the frequent and erroneous argument that it is 'only a theory').
It is only a theory only a Scientific Theory which means that it has passed a certain rigorous set of tests that say that it is accurate enough to use in the development of further theories. This is many orders of magnitude more rigorous than any religious belief (say 10^10 orders of magnitude).
P.S. I am mostly posting this to not use my mod points for evil.
"Starship infantry" would have been better, although given the book's purpose as pro-military propaganda it lacks that romantic haze required to blur away the pointless death and destruction such troops have always created when deployed outside their own borders.
I've never been quite clear as to whether it was pro-military propaganda or straight sarcasm. In reading many of Heinlein's other works I eventually started to believe that it might indeed be the latter. Either way Heinlein must have been a very interesting person (read crazy) possibly in a good way.
You cannot prove that parallel lines do not intersect purely by using geometry. You cannot prove 1+1=2 using math. The former is treated as an axiom, a statement that is intuitively assumed to be true in further proofs. The latter is a definition of terms - given what 1, 2, addition and equality are defined as, the statement is true.
The former is not treated as an axiom it is an axiom and as such it cannot be proven in any system. The latter can indeed be proven if you step outside of the bounds of algebra (which is a field of mathematics that covers addition) and into the bounds of set theory where we have a definition for 1 and a definition for 2 and a definition for the process of addition and using those three definitions we can indeed prove that 1 + 1 = 2. In algebra we would define the addition of our system such that 1 + 1 = 2 at which point it is treated as an axiom. To be clear there are systems where 1 + 1 != 2 (boolean algebra) but we can assume you knew that and were specifically discussing integer arithmetic.
The hardest part of climbing the ladder of success is getting through the crowd at the bottom.