1. The arguer may be right about…, but he seems to neglect(fail) to mention (take into account) the fact that….
2. Although many people believe that… , I doubt (wonder) whether the argument bears much analysis (close examination).
3. It would be possible (natural/reasonable) to think (believe/take the view) that…, but it would be absurd (wrong) to claim (argue) that…
4. A close (careful) inspection (examination/scrutiny) of this argument would reveal how flimsy (groundless/fallacious) it is.
5. However just (logical/sound/valid) this argument maybe, it only skims the surface of the problem.