For you yourselves know, brothers, our visit to you wasn't in vain,
Then again, the passage may be viewed as preventive, rather than defensive. Certainly, when Paul worked to support himself, he did not begin doing so only after slander compelled it, but that was his manner of preventing slander.  Why not view this paragraph in exactly the same way?  That all of this could be apologetic is true enough; but again from Kelcy, "There is not the same certainty"[3] of it here as is evident in Corinthians.