A new report by Ben Southwood, fellow of the Adam Smith Institute, makes the liberal utilitarian case for patent law:

Property rights are good not “just because”, but because of how they contribute to human flourishing
Patents are, like other property rights, an automatic market mechanism making use of decentralised information and robust to shocks, unlike prizes, which require some sort of central direction
Patents encourage information to come into the open, but they limit how you can use that info
Intellectual property rights can be too stringent, but it’s unclear whether we’ve reached that point yet