If a defendant is not guilty, how would not having tougher standard of proof affect this person?

If I understand your question correctly, you are asking
how an easier standard of proof affects innocent defendants.  If so, having an easier
standard of proof would tend to make it easier for an innocent defendant (or a guilty
one, for that matter) to be convicted of a crime.

From a
defendant's point of view, a tougher standard of guilt is a good thing.  If you are
accused of a crime, you would rather have the government be forced to prove you guilty
beyond a reasonable doubt, or beyond any doubt at all.  You would not like the standard
to be a simple preponderance of the evidence.

So an easier
standard of proof would be very bad for an innocent defendant.