Besides attempting to paint all postmillennialists as consistent, i.e. heretical "full" preterists who deny a literal, future Second Coming - despite all claims to the contrary - what other concerns does he raise?
Englesma, whom I normally have great respect for, muddles the water by falsely charging Reconstructionists with a belief that "Christ would come in the second coming within a few years, that is, in the destruction of Jerusalem in A.D. 70", Englesma IMO is deliberately confusing his opponents' view of His "coming in the clouds" (the judgment of Israel) with His Second Coming, i.e. His literal return. No Reconstructionist work I have ever read has ever proposed that the two "comings" are the same event.
Perhaps now we know where our friends gets it from. Reading people who paint with a broad brush when they write about other people.
As mentioned to TC on a different thread, when one is so focused on building the kingdom here on earth, it gets easier and easier to “spiritualize” the return of Christ, and especially since everything else has already been spiritualized.
I would say that post-millennialism is a great danger to post-mil Christians.
That aside, though, I can certainly see how preterism is a HERETICAL danger that will easily betray post-mil Christians.