I believe that it should be totally fine to disagree with the author, as long as it is expressed in a polite way.

After all, most of us is here for meaningful discussions and learning something new. Personally, I appreciate a constructive criticism much more than flattering. Flattering can make me feel good, but a constructive disagreement can provide me with new insights and improve my way of thinking.

Of course, there will always be people who are convinced that they know everything best; those people might get offended by a disagreement no matter how politely it is expressed, but that's really not our fault.

Cheers! : )