Intellectual Monopoly Rights

Update: Can anyone of my readers provide a reason why patents should not be considered similar (from policy and law point of view) to establishing new trade routes?

Johan Norberg writes about intellectual monopoly rights in his blog.

The text of his makes me wonder, would he also have supported the
mercantilist system of giving monopoly for international trade of certain
items or trade routes? Would he consider that it was the right thing to
do, when the trade routes to Asia and America were being created - for a
limited period of time. To be fair, Norberg mostly speaks about copyrights
in his text, but the omission of patents gives the impression of them
being in the same category as copyrights, which he does not condemn.

The reason for asking is the patent laws. Patents are essentially
government granted trade monopolies for establishing a new trade route.
Not in the physical realm, but in the realm of ideas. And they work
exactly the same way as the mercantilist trade monopolies did. Once you
get the monopoly from government nobody else can trade there without your
permission. Not even if they travel there without any help from you or
your original trek.

I, as my readers may know, am opposed to the mercantilist trade monopolies
and see no difference between establishing new idea and establishing a new
trade route in an unknown world. The case for or against copyrights is a
lot murkier, but from liberal perspective, there should be no reason to
create and enforce government legislated monopolies, such as the trade
monopolies of past, or current patents.