I have seen some of the things in Europe yes but I dont think that that quantifies them as being safe. I do not recall claiming to know any facts about the danger of smoke in a stadium, I just gave my opinion.
I think the point he's making, is that if they were harmful there would surely be some information somewhere that explains what the risk is, what causes the risk and what the short term and long term effects would be. I searched all over the place and couldn't find anything.
What we seem to have is people looking at the smoke and assuming it must be dangerous because smoke from fires is dangerous.
Whether or not smoke bombs are dangerous is not a matter of opinion. The fact that they are sold for use by the public and are designed to be used in paint-balling etc for people to conceal themselves and walk through, suggests there is no risk, or at least no significant risk. Therefore it's up to you to demonstrate what the risks are.
And the fact that they are banned does not prove they are dangerous. All liquids in bottles over 100ml are banned on flights - not because all liquids are dangerous, but as a catch-all to deal with those that are.
In some ways, banning them is a greater risk to safety than allowing 'stadium-safe' smoke bombs into the grounds, as it increases the risk that some muppet will smuggle a firework in.