Playing devils advocate 
Disabled toilets came about surely because being in a wheel chair or requiring a higher toilet and having bars to assist with standing was an excellent idea. Ordinary toilets were totally useless for obvious reasons and they have been a massive help for the disabled to engage in social life without the worry of going to the loo, something we take for granted but not for them I assure you.
If you use a disabled toilet you quite possibly will need quite a little bit of time to do the necessary functions and I can assure you people will not want to queue whilst a toilet for general use is being used for 5minutes by somebody needing assistance whether wheel chair bound or not. It will be a retrograde move and there would soon be somebody saying, 'We want separate loos'.
I do think it stupid though if a disabled toilet is free for it not to be used. I don't see why a disabled person can't wait their turn as it's not about quickness but ability to use a wheel chair or high toilet and bars.