Look at the 3D printer inventors from the 1980's who rested on their laurels selling $30,000 3D printers until their patents expired and the open source community started producing them for under $1000. Ten years after the patents expired, you can get a 3D printer for $199 that genuinely rivals the quality of a $30,000 printer just 10 years ago.
There are all manner of incentives for innovation and profit is only one. But locking down ideas in this way prevents others from improving on ideas, and incentivizes one-time innovators to focus on legal battles rather than continued development.
I think these are the questions you should be thinking about when arguing against IP protection laws.
Edit: One thing you failed to mention is that the technology available after the patents expired was orders of magnitude more advanced than what was available in the 1980s. For this reason, it's simply a no-brainer that the cost went from $30k down to $1k.
Then there's the whole "maker" movement that happened to coincide with the development of 3D printers which meant that 3D printers had a decently sized potential market. Go back 5-10 years and people didn't even know what the hell a 3D printer was! So it's only natural that the original inventors didn't invest more in optimizing the design and making it cheaper.
The existing IP structure can be a useful tool and motivator for people, but it also adds in an extra requirement to all software it touches, whether the designers and coders are conscious of it or not - suddenly, there is a requirement that it make profit on top of what it actually is supposed to do. There's nothing wrong with making money - I'm not here to make a Stallmanistic rant about F/OSS. But this type of structure isn't necessary for great leaps in technology. In the past it was useful because that's how access to the development funds were locked up - you had to play under someone else's banner and their rules to bring you idea to the forefront. Software was different because you didn't need a factory to produce it, and while you still need the factory, you don't need any one particular factory anymore to do the production.
Innovation can and does happen just fine without patent laws or financial incentive.
You can bet companied and Universities will still invent stuff if there aren't patents. The companies will do it or acquire it for competitive advantage. The Universities for prestige, investments from companies, creating talented workforce, and so on. Im for software patents, esp on INFOSEC, to be banned entirely as I see no negative impact on high-impact projects.
People would have wanted, and invested in, the development of 3D printers for just the personal desire part. This is how the most valuable R&D works right now - the vast majority of cancer and major life debilitating disease research is being done not by big pharma (who are instead just researching more dick enlargement pills and modified recipes of the same drugs on the market today they can re-patent for 20 years and bribe off doctors to prescribe exclusively by name because they are the most reliable payoffs for their investments) but by university and state level research institution and non-profits dedicated to their research.
The unsettling truth is that truly revolutionary research does not often come out of profit driven R&D labs. Those organizations are arranged to minimize the risk of research, which also dramatically cuts its potential yields by only targeting predictable results that can quickly be turned into government-granted monopoly profits. Its exploitation of a flawed system that takes talent that could be going towards truly innovative R&D that would almost certainly offset at least what would be lost in cutting these (predominantly) leeches out of the industry.
