What danger could mere thinkers pose? According to several ancient sources, the philosopher Zeno of Elea put up quite the fight:
Greek Anthology 7. 129 [From Diogenes Laertius]
“You were wishing, dear Zeno, to kill a tyrant, a good wish
And to free Elea from slavery with his death.
But you were killed when the tyrant caught you and beat
You to dust. Why do I say this? It was your body, not you”
῎Ηθελες, ὦ Ζήνων, (καλὸν ἤθελες) ἄνδρα τύραννον
κτείνας ἐκλῦσαι δουλοσύνης ᾿Ελέαν.
ἀλλ’ ἐδάμης· δὴ γάρ σε λαβὼν ὁ τύραννος ἐν ὅλμῳ
κόψε. τί τοῦτο λέγω; σῶμα γάρ, οὐχὶ δὲ σέ.
From the Suda
“Zeno, the son of Teleutagoros, Elean, one of the philosophers who lived in the same time as Pythagoras and Democritus during the 78th Olympiad. He was a student of Xenophanes or Parmenides. He wrote Disagreements, and Explanation of Empedokles and Against the Philosophers on Nature. They say that he invented dialectic, and that Empedokles invented rhetoric. Some say that he was caught trying to kill the tyrant Nearkhos—although some say it was Diomedon. When he was being questioned by him, he bit down on his own tongue, cut it off, and spat it at the Tyrant. Then he was thrown into a mortar and ground down into a mush.”
Ζήνων, Τελευταγόρου, Ἐλεάτης, φιλόσοφος τῶν ἐγγιζόντων Πυθαγόρᾳ καὶ Δημοκρίτῳ κατὰ τοὺς χρόνους, ἦν γὰρ ἐπὶ τῆς οη# Ὀλυμπιάδος, μαθητὴς Ξενοφάνους ἢ Παρμενίδου. ἔγραψεν Ἔριδας, Ἐξήγησιν τῶν Ἐμπεδοκλέους, Πρὸς τοὺς φιλοσόφους περὶ φύσεως. τοῦτόν φασιν εὑρετὴν εἶναι τῆς διαλεκτικῆς, ὡς Ἐμπεδοκλέα τῆς ῥητορικῆς. καθελεῖν δὲ θελήσας Νέαρχον, οἱ δὲ Διομέδοντα, τὸν Ἐλέας τύραννον, ἑάλω. καὶ ἐρωτώμενος ὑπ’ αὐτοῦ τὴν γλῶτταν αὑτοῦ ἐνδακὼν καὶ ἀποτεμὼν προσέπτυσε τῷ τυράννῳ. καὶ ἐν ὅλμῳ βληθεὶς συνετρίβη πτισσόμενος.
Diogenes’ account of this is a little different:
Diogenes Laertius, Lives of the Philosophers 9.26
“When he was interrogated about his conspirators and the arms he was bringing to Liparas, he informed on all the friends of the tyrant because he wished to isolate that man. Then, telling him that he could tell him something about these things to his ear only, he bit down on [Nearchus’] ear and would not let go until he was stabbed to death, suffering the same fate as the tyrannocide Aristogeiton.”
ὅτε καὶ ἐξεταζόμενος τοὺς συνειδότας καὶ περὶ τῶν ὅπλων ὧν ἦγεν εἰς Λιπάραν, πάντας ἐμήνυσεν αὐτοῦ τοὺς φίλους, βουλόμενος αὐτὸν ἔρημον καταστῆσαι· εἶτα περί τινων εἰπεῖν ἔχειν τινα <ἔφη> αὐτῷ πρὸς τὸ οὖς καὶ δακὼν οὐκ ἀνῆκεν ἕως ἀπεκεντήθη, ταὐτὸν ᾿Αριστογείτονι τῷ τυραννοκτόνῳ παθών.