Voltaire would be against a dress code because, being a man who has written many plays, he would feel that people should be able to express themselves through the way they dress.
Voltaire writes, "I shall never cease, my dear sir, to preach tolerance from the housetops, despite the complaints of your priests and outcries of ours, until persecution is no more."
"What! Is each citizen to be permitted to believe and to think that which his reason rightly or wrongly dictates?"
Voltaire is saying that because one person in a powerful positions says something, it does not mean that it is so and that it is the right thing to do. Voltaire wrote plays in which he had to channel all of his thoughts emotions and ideas into one script. The costumes that are worn by the actors aren't just pieces of cloth sewn together. They signify the character's personality.
Voltaire was frequently on the run for his impulsive decisions tht usually involved him saying something offensive to his current location, a play that enacted something embarrassing a person in a powerful position (the king, perhaps) did, or just getting in trouble with the law. But his actions informed people of his feelings and thoughts; he may not have been pleased with the King's recent decision of raising the taxes. He writes... "I will go even further and say that we ought t look upon all men as our brothers... for are we not all children of the same father, and the creatures of the same God?"
Voltaire would be against dress code because he would feel that people need to be able to express themselves through their clothing.