So people can focus all they want on the toxicity of all of these building materials, but that one point is never really mentioned and I am willing to bet that vapor is not doing your lungs any favors, it may be better than smoke making it the lesser of two evils. If your goal is 100 % safety then eating your herb might make more sense, all of that gunk in your whips, bowls, and wands is coating the inside of your lungs to an extent.
There are people who have been hooked up to breathing machines and oxygen tanks with silicone tubing for their whole lives 24 hours a day, so think about this: An average human being takes 21,600 breaths per day so if only 20-30 inhaled breaths are from vapor I can guarantee that it is not going to make any difference. The chances of us being in the hospital on oxygen is pretty high so I wonder what people will do if they don't want to use silicone, die? The national average hospital stay is 5 days, so that would be 108,000 breaths so if you were on oxygen that means 108,000 inhales through the tubing and let's assume the average vaporist takes an average of 30 inhales per day that would mean the 5 days on oxygen would equal to 3,600 days of vaporizing, almost 10 years worth.
Just like DevoTheStrange said, materials have to be used in the appropriate way and Storz & Bickel proved that their application is safe since they are one of the only companies that tested their air quality, the Volcano uses silicone tubing, even goes through aluminum and plastics, but the tests came back with no harmful substances. So that proof is good enough for me that in that case the silicone tubing does not contaminate the air quality. That doesn't mean I would use it inside the heating chamber but to use it as a inlet air path has been proven to be fine.
There are thousands of little articles like the one above which determine nearly everything in our lives is toxic in one form or another, I bet if you dig deep enough articles might exist where borosilicate glass has found to be bad for you in some way, there are even articles that state hazards of lamp working because the fumes from working with hot glass can be harmful health.