Some people will invent regardless if a system is in place but there will be fewer people bringing those inventions to market. I doubt you have ever been through the prototype and testing phase of a product, it can be very expensive as multiple iterations are needed to get the product ready to go to market, then you have tooling costs where you can go through multiple iterations too. These are iterations that your competitors won't have to go through and can offer the same product for a significantly lower cost. They can charge the same amount and spend the extra cash on marketing or keep it as profits, a luxury the inventor doesn't have.
A patent system is needed to protect inventors, they deserve a chance to make their money back. Unfortunately many companies take full advantage of these protections and use them as market barriers. The best example I know of is due to the greenhouse gass ban on CFC's inhalers, the new propellent used was HFAs and a patent wall was put around them, my son's inhaler went from $15 a month to $150 a month. I'm all for shorting the term to 3-5 years but inventors need to be protected.