Take brexit for example in a truely equal union then the only way brexit should have won is if there was a majority for leave in 3 out 4 of the constituent countries.
So if a few more thousand people in Wales had voted to remain, that should have effectively meant that the people in England - the vast majority of the population - would have had no say, just because of where national borders lie?
Or you can admit we're not a union of equals, rather 4 seperate countries, with very different ideologies, who have to go along with whatever the biggest member wants regardless of the effects it has on our own nation.
From that, you'd think that everybody in England and Wales had voted to leave and everybody in Scotland and NI had voted to remain. By a relatively small margin, almost half of the people in England are also going to be leaving the EU against their wishes. Meanwhile, 38% of Scottish people WILL be getting their wish to leave.
There are only two workable options: either we are a UNITED kingdom of 60+ million people, each with an equal individual vote, or we split however many ways and consider ourselves to be 2, 3 or 4 separate countries.
Even if we did become four completely separate nations (and just imagine the protests of those who voted not to split but end up in the sizeable minority), you would still have inequalities within the resulting nations as populations still tend to be concentrated in relatively small areas. Would you give the combined population of each settlement exactly the same political weight? i.e. if Glasgow overwhelmingly votes in favour of something but Alloa and Ullapool vote against, then their decision goes for the whole country because 2 out of 3 settlements wanted it?