What an eye-opening thread!
To be honest, my first reaction was totally understanding the OP, and I was taken aback by all the accusations of jealousy, though I wouldn't think of anyone as greedy for wanting a really big house and call this or that room unnecessary (though until RTFTing I also didn't really get playrooms).
We are at the moment a family of 5(have older DC who live independently - sort of), relocating and had to rent to break the chain. We originally thought we need to buy at least a 4 bedroom house to survive. But now in the process of buying a 3 bed, though in square footage it's bigger than our former 5 bed (which had a walk through bedroom and 5th was a box room, so was more of a 3 bed size).
I knew even before we started looking, that I wasn't that bothered with having a big house. My set in stone criteria were a biggish garden, because I like gardening and need the space for the kids to run about, also I was very bothered about being directly overlooked, then a kitchen-diner which would fit a sofa in, and at least another separate living room downstairs, and a view (we are buying in an area where due to the topography most of the houses have some kind of view).
When I was viewing the house, we asked the agent why the people were selling. We knew they lived there for 10 years and had two kids and one already left home and another was on the way out. I expected them to say relocating/wanted to be more central/downsizing. So when the agent said they wanted a bigger house, I was so surprised I actually thought it was a cover-up and that a real reason must be that something was wrong with the house (actually it is a massive doing-up job, so there's lots of stuff wrong with the house, but I feel nothing is impossible to fix). It just didn't make sense to me that they raised their family in a large enough(in my understanding) house, and now are moving to a bigger house? What is the point? Now, after reading the thread, I understand better :)
There were some people who sounded a bit bitter/jealous about someone else owning a large house, and there were plenty of people sounding defensive about owning a very big house. A little bit annoying to constantly read "I/we worked hard for it", because it sounds as if it implies that people who live in small houses do it because they simply didn't work hard enough or just didn't prioritise property, when such a big part of the population, esp. young people, can work themselves to the bone and deny themselves everything but still would have no chance of getting on the property ladder.
I almost wish somebody actually came and said, yes, live in a massive house, didn't work hard for it or got it for free. Doesn't give anyone right to judge them or their social responsibility anyway.
Anyway, we could afford to buy a bigger house, and the one we are buying is realistically too small for us esp. if older DC or family need to visit, but until reading this thread I just thought of more house as more to clean, heat, maintain, more of a burden than a gift. We like camping as well(if the weather is good!), and that is, I think, part of the same mentality, enjoying at least temporarily a much simplified life, with no stuff or admin to take care of, with very basic needs adequately taken care of. Of course we enjoy it because it is temporary and we can return to the comforts of the house and beds etc, but I wonder if anyone on the thread who wants and owns really big houses (not through sheer necessity, but because they can) gets camping and enjoys it?
Honestly if I won the lottery I wouldn't buy a very big house, I'd see it as a liability. Anything which we ourselves wouldn't be able to deal with ourselves, without employing people (cleaners, gardeners, housekeepers), I'd find draining rather than empowering.
If I won the lottery I'd buy a house we could manage by ourselves with a view, opportunity to create a massive garden and some woodland.
The only good thing for me about owning a mansion would be an opportunity to share it with family and friends, have massive parties, invite people to enjoy the space and the surroundings too.
But because all that goes with owning a mansion wouldn't suit me, I'd rather (in case of a lottery win ;) ) rent a mansion for days out/holidays for ourselves and family, with all housekeeping taken care of by somebody else...