There are three philosophies justifying intellectual property:
Utilitarian theory says that intellectual property should be protected as is needed to protect consumers and encourage further innovation.
Trademarks protect consumers because without them, consumers could become confused and accidentally buy lower quality products without knowing.
Trademarks also encourage further innovation by rewarding companies who are the first to use a design with the exclusive right thereto. Without this protection, companies would have little reason to innovate when others could copy their work without penalty or having to work themselves.
This theory is advocated by the Constitution in Article I, Section 8, Clause 8—the intellectual property clause.
Locke said that property was created by the creation of value from a common resource by one's labor.