What's offensive is people coming into "our house" as it were -- the D&D game we've been playing in some cases since before some of those people were born -- and tearing it down to build whatever the hell they happen to prefer. They're just passing through, and they're acting like landlords rather than custodians.
Following your analogy...
... D&D is more like a housing development. You have a house there, which you've decorated to your liking. In fact, you and your immediate neighbors have rather similar tastes, so your house look quite a bit alike.
However, you were never the owners of the whole development. In fact, some people you don't much like, who live on the other side, decorated
their homes completely differently. Tastelessly, in your eyes. Why they practically defaced the whole community. But what can you do, except complain? Because while you and your like-minded neighbors might feel a great deal of ownership over the whole development, you are, truth be told, only a few owners among many.
Over the years, new people moved in. Older houses were torn down and new ones erected. You don't much like the new designs. You feel them to be inferior to the originals. A few of them look too newfangled for your tastes. Worse, a few resembled those houses from across the way you didn't like to begin with.
Now you have every right to prefer things the way they were. But it's a fact of life things change. Neighborhoods change. But it's just not right to go around suggesting that the new folks don't belong. They paid their money same as you. The own their property same as you. They probably even
like the community same as you (I hear it's a good place to raise a family). They are, in fact, pretty much the same as you, except you think their new-style windows are awful and the colors painted their house are gauche.