I'm understand. I'm generally in favor of people being able to express controversial opinions held in good faith. But I've been forced to accept that some people just need to be shut up however possible. In this case I'm not saying he should have his blog taken away, but I am saying no one should amplify content like this.
In the abstract, something is toxic if it disrupts or makes impossible desired processes even in very small amounts. Trolling is obvious, conspiracy theories are closer. Some things inherently generate more heat than light, suck oxygen out of productive conversation. You don't have to be a radical leftist (I'm really not at all), you can just watch it happen here or any other forum.