Re: Why isn't everything made of neutrons?

The answer to this really has to do with quantum mechanics, that you have 
to give something up in order to combine the proton and electron into a 
neutron (energy), and conditions are not always right for that to happen.  This 
is why when a neutron ejects an electron you also have to produce energy -- 
the mass of the neutron is greater than the masses of the proton and 
electron together, and the excess appears as energy.  This is what happens 
during radioactive beta decay (emission of an electron or positron from the  
nucleus of an unstable atom).

To give a classical analogy, you could also use this reasoning to predict
that there shouldn't be any planets in a solar system, or stars circling a
galaxy -- everything in these systems should just collapse together under
gravity.  What stops this is the conservation of angular momentum, and in
order to get a  gravitationally bound structure like this to collapse you
have to come up with some way for the excess angular momentum to be ejected
first.
                  
A good reference to look at is Halliday and Resnick's textbook, 
Fundamentals of Physics in the chapter on atoms.