But weight doesn't mean anything. An equal weight man and woman will still be in a totally different class. Also, it's not about what you can do now, but about your potential. Someone who is currently physically within the "male range" will have to do way less to achieve the same performance as someone within the "female range". Mixing them together would be very demotivating to anyone not in the "male range" physically since they'd have to work insanely hard to even beat the less serious men.

Note: I'm using "male/female range" rather than man/woman because gender doesn't necessarily align with physical build.