At least in philosophy (my discipline), people often say 'it can be argued that p' when arguments for p have been produced by others, and these arguments are thought to have considerable force, but it would take the discussion too far astray to rehearse those arguments. It is sometimes worthwhile to say this, rather than producing an argument for p.

This isn't just for people who are already familiar with those arguments for p. Knowing these arguments exist is often importance evidence related to p, and can guide one's future thinking.