There is a lot of empirical evidence showing patents incentivize investment of resources into innovative efforts, such as R&D expenses in large corporations and VC investment in startups. Of course, it's hard to quantify how much innovation this really drives because it's very hard to measure "innovation" itself. The drawbacks of patents include, amongst other things, the potential to reduce follow-on innovation. Again, this is very hard to measure at any meaningful scale.
> To support this point, we can look at the prevalence and utility of Open Source software projects; which work without patent protection.
Open source projects are driven by people willing to donate their efforts for free. (Well, it's not really free, is it? They are, to a great extent, sponsored directly or indirectly by organizations that typically extract value from something other than the software itself, such as, maybe data.) Do you expect that business model to work for everybody?
Not to mention that the vast majority of open source projects actually don't do anything innovative other than just re-implementing known technologies in a different context. There can be a lot of minor, follow-on innovation in open-source projects, but in my experience, the big advances come from other sources, such as academia, startups or corporate R&D labs.