More blocksize essentially means more opportunity to capture transaction fees. This necessarily leads to an incentive to create bigger and bigger blocks therefore considerably increasing the cost of running a full node.
Yes but...
1. non mining nodes are already doing this altruistically.
Less so than ever before and increasing costs will not help.
2. Technology is getting better and cheaper all the time.
Technology would not keep up under a scenario without a blocksize cap. Moreover security systems can not be built on assumptions of technological progress.3. As adoption widens, there may be more nodes coming on board, even if that hasn't happened in the last 2 years
Increased costs makes this unlikely. The number does not necessarily matter, it is the barriers to entry that do4. The more you move things offchain, the more you introduce centralized elements.
The importance is to leave a choice: "Bitcoin is a trustworthy court enforcing contracts between parties. It's possible to take every contract to the judge, but it is rather inefficient." -gmaxwell The simple fact that Bitcoin holds the truth and can rule over and sometimes enforce contrats between user and third-party necessarily diminishes attempt for the third party to fraud.