I went to a catholic school despite being Christian. RE was of course compulsory, but my catholic school is now known as a catholic science college. We're classed as a faith school, and have a large catchment area. We are the best secondary school in the area, obviously not including the grammar school. If we didn't have government spending, we wouldn't have such good results.
I was never taught to be homophobic, or any if what you've been saying, only I was taught religious things obviously as I did RE.
Also, many people are religious, and had they gone to a normal school or college, they may have been bullied, especially if they are full on believers and need a chaple for prayer etc. The only difference between my school and other schools I can see is that we celebrate religious holidays. Themed assemblies where communion is given wouldn't be possible in non faith schools.. Parents probably wouldn't allow it
I think we have to allow a minimum % of non Catholics in.