Why shouldn't someone like John take soma?

In his interview with Mustapha Mond, the World Controller
in Aldous Huxley's Brave New World,  John tells him that he does
not want contentment over truth.  He tells the
Controller,

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Getting rid of everything unpleasant instead of
learning to put up with it.  [Here he quotes from Hamlet]Whether
'tis better in the mind to suffer the slings and arrows of outrageous fortune, or to
take arms against a sea of troubles and by opposing end them...But you don't do either. 
Neither suffer nor oppose.  You just abolish the slings and arrows.  It's too
easy.....What you need is something with tears for a change. 
Nothing cost enough here.

An
anachronism in the New World, John the Savage is the last truly civilized human being.
He does not want comfort at the expense of his
humanity:

I
want God, I want poetry, I wnt real danger, I wnt freedom, I want goodness.  I want
sin.

When John does take
soma, it is out of his terrible desperation; like his mother Linda,
he has despaired of life.  Putting himself into a soma-induced
coma, John escapes artificially when he has been unable to physically escape the ogling
of the Deltas and others from a world entirely abnormal and foreign to him.  His
destruction is not just the destruction of an
individual; it is the destruction of the
individual to Huxley's view of
utopia.