Personally, where I do think it would be nice if it automatically respecced you to the role you were put in for - that's mainly down to my own laziness as I could very well respec before joining, so it's purely quality of life.
I usually queue as healer, but if you have another 1 or 2 well geared healers in the group which inevitably you do, I always offer to respec to dps. More often than not that is welcomed. If it doesn't look like healing is stable, i'll go back - no problem.
Its annoying if people wont switch, but i dont really think you can force responsible behaviour without punishing the people who dont need it.