I have read that before, that nodes are a force in keeping the Bitcoin ecosystem stick to the rules. But I never understood it.

What does running a node on your laptop achieve? If two parties out there agree to call some roll of toilet paper a "Bitcoin", how will your laptop stop them from doing so? One of the two will hand the other one the roll, the other one will say "Thanks for the Bitcoin" and thats it, right? Why would they send TCP/IP packets to your laptop and ask for permission?

You can call an avocado a Dollar, and someone might accept exchanging it for an actual dollar, but try to walk into a shop and pay for your beer with that. That’s what consensus is for.

It is only when receiving money you can affect the validity of that payment, you can refuse to send them the alpaca socks they "paid" for using invalid address outputs.

That makes sense. When you accept Bitcoin payments and run your own node, you vote for the rules that your own node enforces.

But to me it looks like people think just running a node is like voting for the rules on that node. Even if you do not do any business.