[throwawayjava]

The first two sentences EXPLICITLY state the type of arguments that James is responding to. Click on the links in those first two sentences and read the arguments.

The "main argument" of those posts -- i.e., the posts James is responding to, is not that "project-based learning... make[s] learning interesting".

That may be your main argument, but it's not the argument that the people who James is responding to are (mainly) making.