Public opinion is changeable  Unless there is a minimum threshold for valid votes, freak results will occur. If the threshold is too high, on the other hand, then public aspirations may be thwarted, as for example with the Scottish Home Rule referendum of 1979, where a majority of those who voted supported devolution but not enough to get the proposal passed into law. [1]  Furthermore, public opinion changes over time. Once you have introduced the principle that issues of national concern are to be settled by referendums, there will be nothing to stop the same question being put to the public vote time after time.  [1] “The path to devolution”, Scottish Parliament history pages.