Sylvie Von Duuglas-Ittu is a Muay Thai fighter who has been training and fighting in Thailand for the past two years. As in sports in the West, Thailand divides Muay Thai by gender...but many fighting rings, including the famous Lumpinee Stadium, will not host women at all. The ones that do host women require them to enter the ring under the lowest rope, which is an expression of women's position as lower than men and symbolically contaminating (specifically because of menstruation).
In this interesting piece, Sylvie writes about Thai culture and boxing, ultimately coming to the conclusion that Thai culture and religion (Theravada Buddhism with elements of magical animism) can be respected and preserved without treating women as lesser than men. She notes that there are native Thai fighters working to equalize women's treatment in the ring and out of it, but says Westerners often see Thai culture as monolithic and feel like a suggestion of change is disrespectful. She feels they are incorrect, and may not feel insulted simply because they don't understand the symbolism behind the tradition that women enter the ring under the lowest rope. She does not comment on whether fights should be coed.
GreenHunk has been a Muay Thai fighter for the past 7 years. His take on the article was 100% agreement, and he also adds that he thinks fights should be coed: "I think it makes both parties fight harder. It pushes the sport forward for girls who have the potential to compete professionally."