Patents are abused to lock out competition. This can influence an entrepreneur's decision to pursue an idea, and an investor's decision to fund it.
Ideas are often reached independently by different people and companies. It seems unfair that start-ups might be denied an opportunity to pursue their ideas simply because a large company with sufficient legal resource considered that idea patentable, often without the intention to develop it commercially.
Patents were originally designed to protect inventors and startups, but they have become a legal tool used to stifle innovation, typically by much bigger companies.