A text field adds time to type out (which can lose customers, alienate handicapped etc.), all to accommodate an exception, rather than a rule.

I don't care if you have a slider, dropdown, circle, whatever, but for usability, a gender option should have poles that require 0 or 1 clicks to get to (though a text-field for further elucidation is okay). Continuing down this path, the further step is saying a shoe-size option insults amputees and lymphedema victims and should be a text-field...

Edit - Another fact is that the person filling out this form might not be the person described by the form (say for a CRM tool) in which case it matters more to KISS.