What does the following quote from Benjamin Franklin mean?When the people find that they could vote themselves money, that will herald end of...

First of all, I would point out that this quote is not
definitively attributed to Franklin.  For example, I have seen this quote attributed to
Poor Richard's Almanack and it is certainly not
there.

Be that as it may, the meaning of this quote is that
people will, if they are given the chance, vote to give themselves money even if it
means ruining their society.  This thought is somewhat consistent with the thinking of
many of the Framers of the Constitution.  They worried that the common people would use
democracy to pass laws that would help them financially even if those laws would hurt
the country as a whole.

In modern times, you could argue
that American attitudes towards Social Security and Medicare bear this idea out. 
Americans seem unwilling to tolerate the idea of cuts in either of these programs even
though the programs are the major reason for the financial problems that the government
will face in the long term.