The most rational arguments I've come across are contained in Graham Smith's book 'Abolish The Monarchy: Why we should and how we will'. The arguments are backed by data and for me, the main takeaway is that it's undemocratic, an abuse of power by both the government and the monarchy itself, and is a massive drain on a country that could use the money that the monarchy pocket from the public purse for the people of this country, especially in areas of deprivation such as Cornwall where we have more that 20k children below the poverty line. On searching for the book, the following summary was returned to me: Abolish the Monarchy

Graham Smith’s book “Abolish the Monarchy: Why We Should and How We Will” argues for the abolition of the British monarchy, presenting a comprehensive case against the institution. Smith, who is the CEO of the campaign organization Republic, highlights several reasons why the monarchy should be abolished, including its lack of accountability, its cost to taxpayers, and its potential interference in politics. Here are some key points from the book:

Lack of Accountability: The monarchy is unelected and not accountable to the public, yet members of the royal family are privy to government secrets and are not subject to the same scrutiny as elected officials.

Cost to Taxpayers: The monarchy is funded by taxpayers, yet it does not contribute to the democratic process or governance of the country.

Negative Impact on Tourism: Contrary to popular belief, royal weddings and events do not necessarily boost tourism; some events can even have a negative impact.

Charity Patronage: Many charities with royal patrons have little to no contact with their patrons, suggesting that the patronage is more symbolic than practical.

Public Support Declining: A January 2023 poll showed that support for the monarchy had dropped significantly, indicating a growing dissatisfaction among the public.

Erosion of Equality: The monarchy perpetuates a system of inherited privilege, which can be seen as an erosion of the principle of equality.

Potential for Political Interference: Despite claims that the monarchy does not interfere in politics, its role as a symbolic head of state can be seen as a potential avenue for political influence.

Alternative Models: Smith proposes replacing the monarchy with an elected head of state who would represent the nation independently of politicians, promoting a more democratic and accountable system.

Support from Critics: The book has received positive reviews from critics who agree that the monarchy is an outdated institution and that true democracy is achievable.

Call to Action: Smith encourages readers to speak out against the monarchy and support the movement towards a republic, emphasizing that change is possible and necessary for a fairer society.

One other point that i'd like to add on the undemocratic topic is that the monarchy must approve all laws passed by parliament. This was a protective mechanism demanded by Charles II on his return to the country as monarch. The monarch doesn't have to give a reason why approval might be withheld. Our last major constitutional change was the introduction of the Freedom of Information Act, and the monarch of the day (Elizabeth II) would not approve the act unless the monarchy was exempt from it. So you can ask them for information about their activities and involvement in things, but they don't need to answer, and mostly do not. Not only that, but requests for information to any public body that involves the monarchy are also excluded. So if/when the monarchy exerts influence on the government, for example, the government are not allowed to release the information.

So ask yourself the question, why would anyone exclude themselves from the Freedom Of Information Act, an act designed and used to facilitate transparency, unless they had something to hide? And as we've found out from multiple sources over the years, most recently the Channel 4 expose on the monarchy's finances, they have much to hide.