What the country voted on in the 70s was not what the EU morphed into. This would be OK if the changes weren't significant, but they were.
It was essentially a customs union. Then in 1992 the Maastricht Treaty changed it into a political union, or at least laid the foundations of this.
This treaty was ratified by referendum (barely) in a number of countries including France (50.8%). Note this quote on the Wiki by Jacques Delors :
"Europe began as an elitist project in which it was believed that all that was required was to convince the decision-makers. That phase of benign despotism is over." - implying that the UK was in a state of benign despotism before Brexit due to the refusal of the British government to hold a referendum ?
Throughout the 90s and up to Lisbon there was plenty of discussion on whether a referendum should be held in the UK, both on Maastricht and the Lisbon Treaty. I think all parties at some point (including the Lib Dems) proposed a referendum, but all of them either fudged the issue when they did gain or never gained power in order to hold it. This created IMO a huge democratic deficit, which UKIP exploited to gain the referendum promise. It shows our democratic systems are working correctly, even if it takes a long time for them to engage.
If the UK had held referendums on Maastricht or Lisbon at the time of the treaties I am sure we would not be where we are now.
I think there are justifications for holding further referendums on EU membership for the UK. But given the very high bar that has been set against holding previous referendums, I would at least expect that the referendum should be on joining a something significantly different from what currently exists and not just entry into an EU that the electorate has already rejected.
Given the history of our membership of the EU and the country rather than willingly going into the political union being dragged into it by the elites, I don't trust any government to hold an unbiased referendum on the subject. Past history almost guarantees this. I expect if further referendums are held the elites will attempt to gerrymander them in order to get the results they want, probably by shoring up the voter base with "right to remainers" and probably just about any other trick they can come up with.
It's hard to come to any other conclusion if you look back at the history of the political classes trying to persuade the electorate to become members of the EU.