I would hate it. Imagine being cooped up with one set of like-minded people! I prefer to be able to get away and do my own thing
Surely you tend to meet like-minded people wherever you go on holiday? If you go camping, you meet people who like to camp, if you go to an all-inclusive, you meet people who like an all-inclusive hotel, if you go on a city break, you meet people at the hotel who like city breaks. It's the same as on a cruise. You meet people who like to cruise. They come from all walks of life, and all nationalities. And I know that people who haven't been on a cruise tend to imagine they'd be cooped up, but it's really not like that at all.
IME there are very few other Brits, and growing up, especially camping, my DC made friends with French, German and Dutch kids equally happily as if they had been English
You do know, don't you, that it's not only Brits that cruise? We've talked to some lovely people on cruises, from all over the world - Spanish, French, Polish, Italian, American, Canadian, Japanese - so many different nationalities. My kids have made friend with many nationalities. It does help if you sail out of a port other than Southampton though.
Of course, if you don't like the idea of a cruise, that's fine, but there are some very wrong assumptions of how it would be, by people who have never been on one.