In May, Switzerland is going to be having a referendum about a question that it had 2 years ago - because the circumstances and the options available have changed in the mean time.
Of course, no-one is up in arms about this, because this is how mature direct democracies actually work.
Either you have a coherent logic about how, why and when referendums are held - or else whining about what the "democratic will of the people" is is essentially meaningless.
I think that this is a key point; circumstances change, the options available to people change and frankly people change their minds when more facts become available. The fact is that in 2016 the model of Brexit that was proposed was not possible - as many of us made clear at the time - and so asking a question between the status quo and a more precise version of Brexit would be clear. This wouldn't be against the norms of other Westminster system countries - look at the New Zealand electoral reform referendums (the first question was a simple "do you want electoral reform" and a list of proposed alternatives as a second question, then three years later they asked "do you want MMP or FPTP?" - and hell they had a second repeat of that process again a few years ago to double check with people only they stopped after MMP got majority support in stage 1) or the above mentioned Canada situations for examples of that.
To use the democracy argument against a second referendum is very silly in my eyes - that argument could be easily used against having regular general elections for example. There are many reasons to be against a second referendum (and for a long time I was: its divisive and if you can find a solution that meets the result of the referendum without tanking the economy of the country or alienating significant numbers of people then you should compromise and do that instead of asking the question again or leaving a lot of very dissatisfied people) but the democracy one is silly.