2 reasons I drink soy. 1- we are the only species on the planet to feed on milk well into our adult years
2- we are the only species to take it from another species beyond survival

Alot of people have allergies to soy that they don't realize. I went on a no-wheat or dairy diet and used soy milk and protein shakes. After about a month or so, my hair started falling out in almost clumps. It was awful.

Be aware that SOY is one of the top genetically modified products next to corn and wheat. If you dont know that much about GMO's be sure to research it. Also, with cow milk it is best to make sure you buy organic or even raw to ensure that you are not ingesting harmful substances from cows that were given antibiotics and growth hormones...
Almond milk I hear is one of the best....

It depends. Soy milk can be a good replacement for those that are lactose intolerant. There's a lot of pro and contra talk with soy milk due to its high content in phyto-estrogen. I drink quite a bit of it myself, since I'm vegetarian. But there are also other types of plant based milks you can drink like rice, almond (delicious!) and hemp. All are nutritious and equal or less in calorie content than milk.