καὶ πολλοὶ ψευδοπροφῆται ἐγερθήσονται καὶ πλανήσουσιν πολλούς·False Christs were mentioned earlier. False prophets would be individuals who claimed to speak for God but did so falsely. Many would be deceived by their claims. So the argument from popularity (i.e. that something is good because it is popular) is not necessarily a valid argument. These prophets also follow and supplant the disciples who are killed in the previous verse.
and many false prophets shall arise and shall deceive many (Matthew 24:11)
Earlier in Matthew, Jesus talks about false prophets:
Προσέχετε ἀπὸ τῶν ψευδοπροφητῶν, οἵτινες ἔρχονται πρὸς ὑμᾶς ἐν ἐνδύμασιν προβάτων, ἔσωθεν δέ εἰσιν λύκοι ἅρπαγες. ἀπὸ τῶν καρπῶν αὐτῶν ἐπιγνώσεσθε αὐτούς· μήτι συλλέγουσιν ἀπὸ ἀκανθῶν σταφυλὰς ἢ ἀπὸ τριβόλων σῦκα;This whole section follows from Jesus castigating the Pharisees because they said one thing and did something else. Those who do not bring forth good fruits are false prophets and do not speak for God. They should not be followed. Nevertheless, many will be deceived by them and follow them in spite of their never producing good fruits or good works.
Beware of false prophets, which come to you in sheep's clothing but inwardly are rapacious wolves. You will recognize them by their fruits: They did not gather grapes from thorns or figs from thistles. (Matthew 7:15–16)