If guides accepted both would there be an issue? Where you all complaining when boys lost the opportunity to have a male organisation? I don't believe it was because there weren't enough cubs, definitely not where I live or where I used to live 200 miles away. Scouting was way more popular which was why girls wanted to join
I'm pretty certain it was a nationwide recruitment decision for scouting, will Google in a minute.
With regard to opening girlguiding to boys, that would be a different situation. Parents would know it was a mixed sex organisation (and I wouldn't have to pretend to identify as anything). As it is, parents could be completely unaware that their 13/14 year old daughter is sharing a tent with a male.