The very many parents who believed Wakefield and didn't immunise their children prove you wrong. Some parents are scared, and want to do the best, and cannot assess risk, and cannot understand scientific research, and thus are vulnerable to woo.
See also "wifi is dangerous"; "cellphones are dangerous" etc etc.
> the theory of an environmental cause is actually quite plausible.
I have no problem with someone saying "Cot death could be caused by environmental factors. Let's do lots of good quality research to see if we can discover that cause."
Sprott did not do that. Sprott said 'I have found the cause. This is the cause. There is no room for doubt. By not following my advice you are killing babies. By arguing against my advice you are covering up mistakes that you've made, or you are corrupt'.
Sprott says that no babies have died on wrapped mattresses. This is false. Babies have died on wrapped mattresses.
Sprott claims that toxic gases are produced by fungus and the fire-retardant chemicals. This is false - it's not possible to generate those toxic gases unless you do weird things in a lab. (ie, it doesn't happen in the home when the mattress is used normally.)
So what he has done is diverted attention from correct information; made it harder for parents to remember and follow correct information; caused fear and uncertainty among scared people. He has ignored the very clear recommendations against his advice. And finally he's making money off this FUD; he's using the conspiracy theory as a marketing gimmick.
 A really nice overview here: (http://tallguywrites.livejournal.com/148012.html)