I agree with you re: antipopes, but I don't think it applies too well to how "Antichrist" is used in the Bible, which definitely is in a "good vs. evil" sense. Small-a "antichrists" is a somewhat generic descriptor used in 1 John 2 (one of the criterion being that they "[deny] that Jesus is the Christ"), and so it seems to refer to those who actively oppose Christ.
Separately, that passage also refers to "the antichrist" (emphasis mine), who is traditionally identified w/ the "man of lawlessness" in 2 Thessalonians 2 and the "beast" in Revelation. And this figure is pretty unambiguously evil ("man of lawlessness"; "son of destruction"; makes himself out to be God; violently persecutes Christians; makes people have to worship him if they want to buy or sell anything; etc.)—even by secular standards, he's a megalomaniacal despot.
Separately, that passage also refers to "the antichrist" (emphasis mine), who is traditionally identified w/ the "man of lawlessness" in 2 Thessalonians 2 and the "beast" in Revelation. And this figure is pretty unambiguously evil ("man of lawlessness"; "son of destruction"; makes himself out to be God; violently persecutes Christians; makes people have to worship him if they want to buy or sell anything; etc.)—even by secular standards, he's a megalomaniacal despot.