Not my king
Most people who dislike the monarchy make false or fallacious arguments about their finances, however for me the real issue with the monarchy is with Charles himself.
Charles lifelong mentor and godfather of harry laurens van der prost was a child-rapist getting a 14 year old girl pregnant as well as a serial liar, making up his past and changing its details many times.
Charles never disavowed him before or after his death in 1996, made him Williams godfather and in case you're interested - Margaret Thatcher also considered him a friend.
Charles has a history of promoting fake medicine notably through his 1993 Prince's Foundation for Integrated Health which was closed in 2010 for fraud.
Charles also promoted Max Gerson and his false cancer therapy which it would not be an exaggeration to say has killed people stopping them from using effective treatments and blamed them for their sickness.
Fans who do not know much about Charles like to say he is right/good on the environment and yes he was warning about environmental damage decades before it was mainstream.
However, he has expressed support for incorrect 'biodynamic farming' principles which maintains that the vibrational frequency of insects impacts the growth of plants, that farmers should work in line with the phases of the moon. Nutty stuff, but arguably not as empty as buried cow manure in a horn for 7 months, then diluting it with 12 gallons of water. NOTE: At this stage it would now do nothing.
Of course we should expect to less from someone who lobbied Tony Blair to not regulate his homeopathic read:empty and shitty supplements much like Whoopi Goldberg/Mel Gibson in the USA.
Of course you can expect no less from the enemy of enlightenment