Actually, that's not only a fairly weakly implied
argumentum ad populum, as it doesn't actually argue that the number of ignorant people are small or the number of non-ignorant people are large (though the use of "only" might imply that.)
"The only people who disagree with this statement are people who are simply not informed" is more directly argumentum ad hominem, and, particularly, abusive ad hominem.
http://courses.csusm.edu/fallacies/abusive.htm
Its also, simultaneously, petitio principii since claiming that disagreement with an argument can only be due to ignorance to support an argument is equivalent to claiming that the argument is true to support the argument.