It wouldn't stop me from joining a company that's clearly better than the rest. But engineers have a lot of comparably good options in hub cities, so it's reasonable to be picky about small stuff - we can afford to be. A formal dress code does have real downsides: it (1) costs money, (2) wastes closet space (it's a premium in NYC!), and (3) makes biking to work or otherwise living a pre-/post-work active life more of a pain.
Here in Seattle absolutely everyone would give you dirty looks. I don't trust anyone in a suit, and I don't think they make a man look anything other than sleazy.
Different cultures, different perceptions. Tech culture as a whole does not share the NYC mentality that suits are a reasonable norm. Dress codes just don't jive with a need for authenticity. Give me the weird guy wearing a kilt over the slick sales guy in a suit any day.
I'm fairly active and don't care for feeling hot in the summers or restricted in general. Feel free to rock your own suit, but it's not a "mistake" to disagree with you.
It is not about being forced to wear clothes. It is about working with a management team who is so incompetent that they would do something so stupid as implement a dress code.