Yes you will often get objections no matter what you say. However in the UK, under the Gender Recognition Act it's a criminal offence to reveal that someone is trans ( http://www.equalityhumanrights.com/advice-and-guidance/your-... ).

Designing a database system, and leaving a criminal liability open like that, is very unprofessional.

Not to mention that Data Protection Law in the EU requires you to store accurate personal data, and allows the person to have this data corrected (i.e. you have to change it if they tell you & can prove it). So you may think "We'll just lump you in the 'Transgendered' Category", however if the person says "I'm male, here's my birth cert showing male", you are legally required to change it.