Sauron should be thought of as very terrible. The form that he took was that of a man of more than human stature, but not gigantic. In his earlier incarnation he was able to veil his power (as Gandalf did) and could appear as a commanding figure of great strength of body and supremely royal demeanour and countenance. But at the beginning of the Second Age he was still beautiful to look at, or could still assume a beautiful visible shape – and was not indeed wholly evil, not unless all 'reformers' who want to hurry up with 'reconstruction' and 'reorganization' are wholly evil, even before pride and the lust to exert their will eat them up. But many Elves listened to Sauron. He was still fair in that early time, and his motives and those of the Elves seemed to go partly together: the healing of the desolate lands. Sauron found their weak point in suggesting that, helping one another, they could make Western Middle-earth as beautiful as Valinor. It was really a veiled attack on the gods, an incitement to try and make a separate independent paradise.
from the Letters of J.R.R. Tolkien
I can't decode the bolded line. I tried to replace not unless with only if or if but those didn't seem to make sense.
Given the context and other relevant information these seem to be true: Sauron was not wholly evil at the beginning of the Second Age; In a point of view he was a kind of "reformer" hoping the well-being of all inhabitants of Middle-Earth before his corruption.
To me, it would feel make sense if not unless turned to unless. From the context the bolded line seems to mean like this: ...in fact was not wholly evil, unless all eager 'reformers' are wholly evil when they didn't start to corrupt yet.
I can't find at which point I got confused. Please help!