I will be looking into more about the writing of Simon Oxenham

Definitely! By the way, he's @simoxenham on Steem.

do you think that all research papers should be published for free?

I think the scientific record should be freely available under an open license. This would allow anyone to access and reuse scientific publications, datasets, and software. For science to rest on a healthy foundation, I think it's important to have these basic building blocks be open. Furthermore, most science of this category is publicly or philanthropically funded. All of the stakeholders (besides publishers looking to extract profit) want the research outputs to be open.

Now this doesn't mean that publishing is free. Of course, sometimes there are costs, although experiments like Steem show that costs don't need to be paid by paywalls. In the open access model for scholarly publishing, oftentimes the authors (usually their grants / employer) pays an APC (article processing charge) to fund the publication process enabling the resulting paper to be distributed for free. While this system has a ways to go in becoming cheaper, it creates a much better foundation for science.