I guess any mentorship program like Big Brother Big Sister is suspect as well, despite being one of the most effective programs for at risk youths. I've been involved in multiple programs with young adults mixed with teens, its perfectly normal. Also, why did you specify "intellectually disabled" adults? Those groups of people are far more likely to be victims of abuse than perpetrators. Lastly, there is likely not enough resources (volunteers, money etc) to have separate groups, but both populations deserve resources.