Do people think that there should be a minimum garden size to house a pet?

Obviously it would be in relation to the size of the pet.

For instance a larger garden size for a Great Dane compared to a Jack Russel.

I think it depends what you are using the garden for I.e. if you have a small garden but exercise your dog regularly outside of it then I don't think it matters.

No. With cats, a lot of people keep them indoors. So wouldn't make any difference then.

Cats just jump over the fence anyway so it doesn't matter what size the garden is. My cat is rarely in my garden,

Not if you own goldfish, lol

no a lot of larger dogs need less space than medium or small dogs, some large breeds in particular do perfectly well in flats as long as they have appropriate owners that exercise them a garden is irrelevant for some dogs

You sound like Lance-Corporal Jack Jones from Dads Army!!!

A minimum sized forums to size some massive ego's might be much better