Will bad homebrew kill me or make me blind?
First of all, the answer to the question for the beginning homebrewer is no.
Most beginning homebrew books say something along the lines that no microorganisms that can hurt you can live in beer, citing beer's low beer is much safer than drinking water from a disease standpoint; that's one of the reason beer has been a popular drink throughout the world for so long. In a few extreme cases, heavily spoiled beer may cause diarrhea or stomachache, but the beer will be foul enough to be undrinkable. As long as you don't drink anything that tastes spoiled and unpleasant, you should be able to avoid this.and content. In general, drinking
As for blindness, adulturated moonshine (a distilled, not fermented, spirit) sometimes contains denatured alcohol, which can cause blindness and death. This is not a risk inherent to distillation; bad moonshine was the result of the underground distilling economy that grew out of Prohibition in the United States, where unscrupulous and unaccountable distillers used "denatured" alcohol, alcohol intended for industrial uses which has been poisoned to discourage people from drinking it, to increase their output. This is simply not a possibility with beer, unless you're deliberately pouring methyl alcohol or rubbing alcohol into your brew kettle.
That being said, there are a few cases where advanced home brewers need to be careful to avoid really dangerous bacteriological contamination. Beginning home brewers are unlikely to encounter these problems.
Some brewers like to can their wort, usually so that they can make an all-grain yeast starter later on. As with any canned product, botulism is a concern. Home canners should always use safe pressure-canning techniques, as they would with any other high-sugar solution they were putting up.
Brewing with Rye
Rye, an uncommon but not unheard of brewing grain, can sometimes be infected with a parasite called ergot. Ergot contains a toxic substance called ergotamine, which when ingested can cause a syndrome called "St. Anthony's fire", which may include LSD-like hallucinations (ergotamine is an LSD precursor), convulsions, and death. Ergot infection is rare in modern rye supplies, and it is not clear whether it can survive in beer, but brewers who grow their own rye should take special caution.
Brewing with Herbs and Plants
Obviously, one way to make your beer poisonous is to put poison in your beer. Adventurous home brewers should remember that many common plants, even plants that are sometimes recommended as "herbal remedies", can have serious toxicities or drug interactions; for example, St. John's Wort, one of the most commonly prescribed "medicinal" herbs, can have serious and possibly life-threatening interactions with some antidepressants, antibiotic and antiviral medications, and can prevent some birth control medications from working.
Brewing with food plants and culinary herbs is generally safe, but if you're getting your ideas from a "medicinal" herbal rather than from a cookbook, don't serve it to anyone unless they know what they're getting.
Brewing with Meat
Yes, believe it or not, there are traditional beer recipes that call for the use of meat; for an example, see the entry on Cock Ale. Should a brewer want to attempt one of these, additional bacteriological precautions would probably be a good idea. In the case of Cock Ale, for example, the meat is cooked first, then soaked in a stronger alcohol solution than the finished beer before being added to the secondary fermenter.