Obviously it depends on the situation. If someone asks you " I have a re-wireable fusebox, does it need changing" Then the answer is no.....Unless, are they having alterations and additions to their installation? Do these alterations require RCD protection? Then quite possibly a board change is the most practical and economic way to provide compliance.
I think it's jumping the gun to assume that if someone is advising a board change, then they are trying to force people to have work done that they don't need. Each situation is different and should be assesed on it's individual merits.
Another way to approach it is to say something like "No, your fusebox dosen't have to be changed, it isn't illegal, but the modern consumer units offer a higher degree of protection and are simpler to operate".
No forcing, no lying.