It tells you to "suit up head to toe" before using it because it's the safest way to do it and it doesn't know if you're going to spray a dozen 25-gallon tanks in 1 afternoon or just use 1/5th bottle in your back yard.

Labels for approved pesticides/herbicides are a sort of contract and letter of the law for it's approved use. Labels (and especially MSDS sheets) can make some really ordinary commonly-assumed-safe stuff sound absolutely scary.

Fwiw, very few people are sensitive to BT, even applications of large amounts...still, if you're going to hook up a pipe to a 500 gallon tank to spray you should probably be wearing a particulate filtering mask, eye protection, gloves, and long pants/shirts.

It can KILL other organisms. Why are you surprised it has warning labels?

If you have a bad experience with it, the lawyers want to be able to point to the label and say, "We warned the users."

ONE: There are MANY things that aren't hazardous AFTER they are applied or spread that you need protection against during the mixing and application process because you are being exposed to a higher concentration.

Also, if you are mixing from concentrates - concentration matters. Compare the MSDS for household vinegar with that of glacial acetic acid, or baby shampoo with the sodiuym laureth sulfate concentrate that goes into it.

TWO: It is LIVE BACTERIA! Even Bacillus subtilis, which is widely used because it is so low virulence, if inhaled as a mist or aerosol, might cause a problem in your lungs. BTW, a toddler or pet drinking the concentrate, if the spreader/sticker didn't make then vomit, could have some spectacular diarrhea from the bacteria altering their normal flora. Not likely to be fatal, but miserable. It has been associated with outbreaks of food poisoning.

THREE: If you are immunocompromised (HIV, chemotherapy, using steroids for asthma or arthritis) or if you have chronic lung problems, the last thing you want is a snootfull of live bacteria. Bacillus subtilis is not classed as a pathogen, but it has caused infections and septicemia on rare occasions.

FOUR: "Repeated exposure to high concentrations of microbial proteins can cause allergic sensitization" Yes, just like any other antigenic substance, so cover up and mask up while handling it.

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Relevant publications:

http://serenadegarden.com/wp-content/themes/serenade_garden/labels-msds/rtu-label.pdf
http://serenadegarden.com/wp-content/themes/serenade_garden/labels-msds/SG-RTU-MSDS-061610.pdf

http://serenadegarden.com/wp-content/themes/serenade_garden/labels-msds/con-label.pdf
http://serenadegarden.com/wp-content/themes/serenade_garden/labels-msds/SG-CON-MSDS-062210.pdf

One of the reasons I garden organically to avoid hazards to my skin and lungs, etc

This is a fairly common misconception about organic products - they are not necessarily entirely "safe". Diatomaceous earth, pyrethrum, nicotine based sprays, even horticultural vinegar can be quite harmful to those applying such materials unless appropriate safety precautions are taken. Even some common soil amendments can cause respiratory issues or worse if the substance is inadvertently inhaled or comes into skin contact.

Simply because some product is labeled "organic" or "natural" does not mean it is safe for humans. The purpose of these products is to kill something and that could mean you as well. Due care in use of any insecticide, herbicide, or fungicide is necessary because some of these products can cause severe harm if they get to the wrong place, such as your lungs.
Serenade Garden is a bacterium, "Bacillus subtilis" and like any other bacterium can, in the wrong place, cause severe health problems. Far too often
I read from people that this (name a product) is organic or natural and will not hurt you. That is the same thing we were told about DDT.

Ha! I ordered BT once, and then read the label and decided I'd rather keep on squishing the cabbage worms and returned it.

My niece and nephew grow kale for Whole Foods. They spray BT with a huge hose, and of course are suited up for the the job. However, I work with them sometimes, and there is never a concern about being in the kale fields at harvest time.

Thanks for the explanations above, folks. Now I more fully understand the reasoning behind the labels, and the times to be protected and the times to relax.