To expand Heathrow is to send a message to the world that Britain is open for business after Brexit.
To do so at the cost proposed is to send a message to the world that we've lost our marbles and our politicians can't cope with primary-school arithmetic.
Large infrastructure projects in the UK will send a powerful message.
Where the benefits exceed the cost of provision by a prudent margin, yes. Otherwise our 'powerful message' will be met with utter bemusement.