Nothing is wrong with soy as a source of protein for chickens...
The list of reasons soy is not popular is long and little of it has anything directly to do with a chickens health.
Here are a few of my personal reasons for being as soy free as possible.
1. I am opposed to what agriculture has become in this country. The "industrial machine" only concerned about profit and control. I trust nor like anything Monsanto Corporation does! Monsanto holds the patent for genetic modification that know effects all but organic soy!
2. GMO genetically modified organisms. I am deeply concerned about the long term impact. Also I am opposed to the idea that seed can be patented and owned! Hence giving one company power over the worlds food supply.
3. Mono cropping corn and soy has detrimental environmental impacts. It is the opposite of diversity.
4. It is almost impossible to go to the grocery store and buy food that does not have corn or soy hidden in the ingredients. We inadvertently eat way more corn and soy than any culture in the world. We are the fattest nation on earth and one of the most unhealthy. So I avoid processed foods, to avoid corn and soy. (Here is where chickens come in: I avoid soy in my chickens diet, since I eat the eggs and the meat. I also avoid it to vote with my pocket book and not give money to the companies and system I oppose.)
5. Serious heath issues are starting to crop up with the over consumption of soy.. It appears it may effect hormones, causing all kinds of problems in children and adults.
(No Asian cultures do not eat much raw soy, they consume mostly fermented soy.)
Not to get off topic, but are you sure about the formula? Both my daughters couldn't have milked based baby formula when they were little, and were fed soy formula instead. It wasn't that long ago. lol
I think all the hoo haw about soy is just plain silly. Soybean meal is added to feed to increase protein levels. Traditionally, either soybean meal, cottonseed meal, or linseed meal is added for protein and the deciding factor on which to use is price. Whichever is the cheapest meal that week goes in the mix. The only time I have a problem with soy is when it is added to milk replacers. The babies cannot digest it very well if at all.