By a quirk of the calendar, the next eight days will bring two defining national events. One will give the people of Britain a chance to express themselves on the system under which the country has been run for longer than anyone can remember. And the other is the AV referendum.

No one should be surprised that the royal marriage has garnered more attention than a plebiscite on our voting system – or that the collective reaction to Friday's wedding may well reveal more about us than the ballot on the alternative vote six days later. That's partly a testament to the enduring hold the Windsor family exerts on our national imagination, but largely a function of an electoral reform that is described even by its chief advocate as no more than a "baby step in the right direction". (That is Nick Clegg's description of a change he once indirectly referred to as a "miserable little compromise".)

Which is why perhaps the most astute verdict on the referendum campaign has borrowed Larry David's verbal shrug to declare neither Yes to AV, nor No to AV, but rather Meh to AV. It's hard to get excited by a change that is little more than a tweak to our current method of counting votes, that promises nothing so grand as proportionality, that still plays a winner-takes-all game in which 50%+1 majorities are all that count.

AV can't even provide the clarity of a partisan boost one way or the other. The evidence about which of the two main parties would benefit is murky; most experts believe that none of the decisive electoral outcomes in the postwar era would have turned out differently under AV, with some variation only in the most borderline cases. Perhaps this explains the vitriol hurled in recent days by the yes and no campaigns, which happen to map broadly on to the two partners in the coalition. As Henry Kissinger observed of academic politics, they are vicious because the stakes are so low.

That view, though tempting, is surely mistaken. Next Thursday's vote will have consequences, starting with a shift in the balance of power within the coalition. If yes wins, David Cameron will lose face in the eyes of the Tory right, adding to his failure to win a general election a year ago. He will be in no mood, and no position, to cede more ground to the Lib Dems. If no prevails, then it will be the Lib Dems who will need placating: some are quietly looking forward to a defeated Clegg demanding Lords reform to soothe his troops, a consolation prize that could prove shinier than the original trophy.

And, whichever way it breaks, the coalition will need healing. I initially shared the cynicism about the recent run of Tory-Lib Dem rows, a spate of spats conveniently timed before polling day to persuade the faithful that neither side had rolled over to the dreaded other: a coalition insider has conceded to me that some past bust-ups were indeed "pre-co-ordinated". But when a cabinet minister accuses his own chancellor of lying – as Chris Huhne has done in a letter to George Osborne – the notion that this is entirely stage-managed loses plausibility. However it started, the coalition's future credibility is seriously damaged now that ministers have publicly accused their closest colleagues of "lies, misinformation and deceit".

Labour voters are not mere onlookers in this: the pollsters reckon that with Tories and Lib Dems broadly aligned on each side of the divide, it's the Labour vote that will swing it. Given all that, what's a Guardian reader to do?

For the tribal Labour supporter, there is, to repeat, no clear arithmetical upside or downside to AV. Humiliating Clegg would provide an instant sugar rush, but it would come at the cost of strengthening Cameron – who is, don't forget, a Tory prime minister. This may be one of those rare occasions where a political decision is best reached not by calculating selfish advantage, but by weighing the actual arguments.

The no case has been put vigorously, with the Tories helpfully reinforced by Labour's old guard. It argues that AV costs big bucks, helps the BNP, unfairly gives some people more votes than others, leads to coalitions, and prompts politicians to huddle together in the bland middle.

Happily, most of those arguments don't wash. AV won't cost more, because ballots will still be counted by hand not by expensive machines. It won't help the BNP, who will have next to no chance of winning a seat under a system that requires candidates to appeal to supporters of other parties: that's why the BNP is urging a no vote.

AV does not give some people multiple votes: it will be one person, one vote in each successive round – whether for your original choice, if that candidate is still in contention, or for your fallback option. In Lib Dem Jo Swinson's memorable analogy, if I ask you to get me a Mars from the canteen, or a Twix if they've run out of Mars, then I still only get one chocolate bar. As for the claim that AV leads to more coalitions, the number-crunchers say that's far from clear. Of course this argument would be easier to swallow if it were not coming from Tory ministers serving in, er, a coalition government born under first-past-the-post.

The most powerful objection is the one from the left, arguing that AV will see both Labour and the Tories chasing the second preferences of the remaining rump of Lib Dems, "Orange Bookers … [who] now favour Conservative over Labour", thereby tilting our politics rightward, according to Labour blogger Anthony Painter. The trouble is, as Painter concedes, the current system already pushes the main parties to chase after a sliver of centrist voters – so voting no doesn't much help.

Of course AV is miles from perfect, even if it does allow voters to express more fully their true preferences; most reformers would prefer PR. But it's naive to think that defeat next week would keep progressives' powder dry, allowing for a future push for full-blooded electoral reform. That's rarely how politics works. It's success, not failure, that breeds success.

That lesson was taught in 1999, when Australia held a referendum on whether to remove the Queen as head of state. The alternative on offer was another "miserable little compromise" – with MPs, not the people, electing a new head of state – and some republicans preferred to let it fail and wait for something better. They're still waiting – and Elizabeth II is still Queen of Australia.

Which brings us to the royal wedding and its unlikely connection with the AV vote. The monarchy remains strong in Britain partly because it answers the genuine human need for continuity. Yet sometimes continuity can feel like paralysis, as if we are powerless to change our country even when we want to. The stubborn longevity of an unelected House of Lords, despite a century of attempts at reform, is the clearest example. The most depressing anti-AV arguments suggest we have to stick with first-past-the-post because that's how things have always been done – that, in the words of John Reid, anything else would not be "British".

That's a depressingly frozen view, one that would deny today's Britons the right inherent in every democratic society: to be masters of our own fate. I'll be voting yes next Thursday to break the taboo that says our creaking, outdated and unrepresentative electoral system – which can grant large majorities to parties who win just 35% of the vote – is too sacred to be changed. Once we've shown that it can be improved, even a little bit, we can improve it again. But first we have to break that taboo.

freedland@theguardian.com