I think we have to make a distinction between close family relationships and strangers. Obviously, it is never OK for strangers or acquaintances to offer opinions on our lives.
In a close and warm family there is leeway for people to "speak into" each other's lives -this is part of relational intimacy. However, that kind of intimacy has to be earned with trust and respect. In my own family, I call my FIL "dad" just like my DH does, and if he was concerned that we were doing something foolish, he would probably go to DH, but he might also come to me. Even if I disagreed with him, I would not think he was out of line for broaching the subject.
It's just hard to make blanket statements without knowing the people involved. Obviously the conversation was annoying to the OP, but that does not mean that the father in law was necessarily doing wrong by talking about it. It just depends on the relationship.
However, as I said before, calling people "silly" or "crazy" is definitely rude, and there may indeed be a lack of respect/trust going on. That's a different situation.
When my FIL wanted us to buy a house because we were having a second child, he brought that concern to me as well as to my husband.
I actually saw it (in his case) as a gesture of respect, because he knew that I was part of every decision. And he knew he could talk to me.
He also knew that I would "hear" him--sometimes his son (my DH) will cut a conversation off abruptly, which leaves him worried that his well-intentioned concerns and advice are simply being brushed aside. I, on the other hand, am better able to explain our priorities ("I don't have time to keep my bathroom clean--when will I have time to take care of a yard? Right now I don't have to remember to take the garbage out every Thursday night; with 2 kids, I really don't want that responsibility.")
Then he dropped it.
So I think that's perfectly reasonable exchange. Haranguing isn't, but I think it's not that horrible for someone's parent (their first "life coach") to raise some concerns.
yeah, various people might inform me of vacations and purchases that seem like a waste to me. I am sure some have felt the same about some of mine over the years. It isn'tmy job to critique the decision. If I can't give it ringing endorsements I should probably limit it to "Oh, that sounds interesting"
The flip side of this is: I've had plenty of people tell me that they didn't approve of a decision--my FIL and the house thing, above. It was mildy annoying (occasionally informative), but it's not like "them criticizing me" or even "them pressuring me" meant I had to DO anything about it.
I don't have to do what they say. And I don't have to worry about what they think. My FIL thinking we should have bought a house and that we were foolish not to doesn't change our relationship
--because he *and I* don't let it change the relationship
He disagrees with me. Oh, well.
He mentions this disagreement. Oh, well--dads do that sometimes.