What is your opinion on using rhubarb leaves, tomato stalks and other materials considered toxic, in the compost?

It depends on how 'hot' your compost pile is. At a hot enough temperature, and with enough processing time, the oxalate in rhubarb leaves would dissipate and any diseases on tomato stalks would be cooked. If you're turning your compost often enough, using Rot-It and keeping the pile moist, you're OK. If you're a cold composter and just let things sit there for a year, I wouldn't use either of those two products in there.