I was well aware that gliders fly in cloud - because ChrisN told me so many years ago. I discussed it (and many other related topics with him), and learned a lot from a highly experienced and concerned pilot.
Those who wish to impose restrictions on glider pilots are, in my view, missing the point. The risk of collision with gliders in cloud outside controlled airspace is very low - far lower than the risk of hitting another powered aircraft flying in the same IMC.
Commercial aircraft really shouldn't be there at all - they have all that dedicated controlled airspace that we need permission to enter. That risk should be zero.
What frightens me far more is watching power pilots blunder through gliding sites blissfully unaware of the chaos and distress they are causing. Surprisingly, I can't recall ever having read of a MOR or Airprox filed by a glider in those circumstances. Perhaps they are too forgiving of us power pilots?