We never had a referendum on creating a political block so NF was quite within his rights to campaign to leave it.
This time it's entirely different we've had one to Leave and now we're told we should simply have another one as the first went the wrong way.
Are you saying that if leave had lost 52-48, Farage would have just gone "fair enough, that's that then, carry on with the EU, I'm going to go help Clinton"?
The country is deeply divided. Many people still strongly believe that leave / stay is the only way people should have voted. Many people still believe that people were misinformed. Many still people believe that the leave didn't clearly state their plans for the break up. All of those factors are going to lead to large numbers of people wanting a re-run - and would have been the case regardless of which side actually won.
Personally I don't see anything undemocratic about parliament getting a say in the plans for our departure, or even a referendum when we actually have a concrete plan about what we're going to do. In the same way as if we had a general election next week, and a pro-EU party won on a pro-EU stance it wouldn't be undemocratic for that party to call the whole thing off.