If you mean those ‘left behind’ are referring to back-sliding Christians then I would have to strongly disagree. What father would leave behind his weaker child to suffer hell on earth? Christ didn’t suffer on the Cross for the sinless.
If you are referring to the ‘left behind’ as the lost then you bring an interesting point. There are two camps: one that believes the antichrist is revealed prior to the rapture; and the other group is dogmatic that the antichrist will be revealed AFTER the rapture.
So if then the AC is revealed prior to the rapture, then the passage in Rev. 13:18 makes sense, as it is a warning to the wise, discerning Christian, otherwise it would be possible that the elect of God could be fooled by this evil man. There are a lot of evil leaders out there, but just one will be identified by the number 666.
On the other hand, if the AC is ‘revealed’ AFTER the rapture, who is he being ‘revealed’ to? The damned? Those poor folks will be given over to the grand delusion according to Scripture, as they are damned by their own rejection of Christ. What will be their purpose then of decoding the name of the evil man, counting to 666, by the passage in Revelation 13:18?
2Th 2:8-12 KJV -  And then shall that Wicked be revealed, whom the Lord shall consume with the spirit of his mouth, and shall destroy with the brightness of his coming:  [Even him], whose coming is after the working of Satan with all power and signs and lying wonders,  And with all deceivableness of unrighteousness in them that perish; because they received not the love of the truth, that they might be saved.  And for this cause God shall send them strong delusion, that they should believe a lie:  That they all might be damned who believed not the truth, but had pleasure in unrighteousness.