Well ... if you can your pre-made starters (in jars) and don't properly sterilize them with a pressure canner, they can get Botulism. Make a starter out of that, and pour it in your wort and .... I sure wouldn't want to drink your beer.
I disagree, Botulism can NOT live through the fermentation process. In the one and ONLY study that was sited on this very subject, they inoculated the wort with the botulism spores, let the botulism take hold AND then fermented UNBOILED wort.
Meaning they intentionally made sure the toxin was present before the fermentation. Even if you are a real wort starter brewer AND a no chill/pitch the next day brewer, the botulism will not have grown in a large enough quantity to be dangerous in the volumes of liquid we use.
So, in a lab environment when someone intentionally inoculates to get botulism into a small amount of wort, lets it take hold, then ferments the unboiled wort it is possible.
Unfortunately, no brewer on earth makes beer this way... IF this was not true there would be a number of cases that this happened to "X" people. Should you be able to debunk my statements or produce ANY evidence that this HAS happened with home brewed beer, wine or mead I will change my tune, until then this is a bigger myth than unicorns...
Dangers -
1. Using a glass carboy that breaks, slicing you open. Think it can't happen? Ask around HBT if anyone has gotten hurt.
2. Being careless with a propane burner. Carbon monoxide poisoning. Knocking over a kettle, when the burner is precariously perched on bricks.
3. Being careless with an Erhlenmayer flask and microwaving the starter, then shaking it and having hot liquid squirt you, burning you.
4. Being stupid with a kettle of boiling wort, after flame out, and trying to carry it.
^^ these are all good points!