His fear is that Swartz's actions will provide more ammunition to open access opponents:
Finally, and most importantly, this kind of action is ineffective. As Peter Suber predicted in a trenchant post that we can now see as prescient, it merely has the effect of tying the legitimate, sensible, economically rational, and academically preferable approach of open access to memes of copyright violation, illegality, and naiveté. There are already sufficient attempts to inappropriately perform this kind of tying; we needn’t provide further ammunition. Unfortunate but completely predictable statements like “It is disappointing to see advocates of OA treat this person as some kind of hero.” tar those who pursue open access with the immorality and illegality that self-proclaimed guerrillas exhibit. In so doing, guerrilla OA is not only ineffective, but counterproductive.
Note -- the Suber post begins with a guerrilla manifesto attributed to Swartz -- but Suber goes on to take issue with the illegal acts advocated.
I have three basic reasons: (1) OA is already lawful and doesn't require the reform or violation of copyright law, even if it could leap forward with the right reforms. (2) OA activists will never match the publishing industry's funds for litigation. (3) One of the most persistent and harmful misunderstandings of OA is that it violates copyright law. We've come a long way in educating policy-makers out of that misunderstanding. But the Orwellian Fair Copyright in Research Works Act (a.k.a. Conyers bill) is just one recent piece of evidence that we still have a lot of educating to do and that publishers can still make a lot of hay from the misunderstandings which remain. A campaign to give the publishing lobby its first valid evidence that OA violates copyright is the last thing we need.