Patents and trademarks are the only ways to create legal monopolies. They are/were intended to reward innovation but despite good intentions are abused.

Not exactly. For example, Major League Baseball has been granted an anti-trust exemption by the US Supreme Court, because they said it was not a business. In some cases in which firms have been found guilty of violating the anti-trust laws, they were fined amounts minuscule in relation to the profits they gained by operating the monopoly. Various governments in the US outsource public services to private monopolies, and the results have sometimes amounted to a serious restraint of trade. The chicanery goes back a long way. For the first decade or so after the passage of the Sherman Act, it was not used against the corporate monopolies that it was written to limit; it was invoked only against labor unions trying to find a way to get a better deal out of the firms operating company stores and company towns etc, etc. Then Teddy Roosevelt, the so-called trust-buster, invoked it under the assumption that he could tell the difference between good and bad monopolies and that he had the power to leave the good monopolies alone. 120 years later, we are in the same sorry situation.

Intellectual property restrictions cause harm even when used as intended. They are an extreme rest restriction on market activity and I believe they cause more harm than good.

Patents, trademarks, copyright, deeds and other similar concepts are part of what makes capitalism what it is, without them capitalism will not work because they are the mechanisms that enforce private property.