Well many reasons ....but one of the main ones and the one that's connected to my heart is the terrible treatment of cows in dairy farms. It is very difficult to ensure that Cows are not treated appallingly. Even supermarket branded 'organic' milk is not free range, meaning that the cows still get little to no time outside their tiny pens. You have to research any dairy brand to really check if the animals are being treated well before you buy the product.
In addition to this, the milk has to go through many chemical treatments due to the high levels of puss in the milk from untreated mastitis infections in the cows udders due to over milking.
*teared up when the calf is being wheelbarrowed away and the mother is chasing it despite just having given birth, so moving.
Milk does undergo treatments to make it 'safe' for human consumption, it needs to be heated to a certain level to kill off harmful bacteria... connection to women not being able to eat unpasturised cheeses here.
The thing is cows milk is intended for calves, calves have four stomachs and are made to be able to digest milk. There is a lot of speculation in some medical circles about the harmful effects of some of the micro bacterium in milk.
Despite all of this the majority of doctors will encourage you to drink it. I'm really fed up of hearing how 'good' the stuff is. I think it's a terrible industry.