Many people are aware of the incident that occurred yesterday when a police horse got scared in a riot in London and ended up throwing a police women of its back and trampling somebody. It is commonly known and scientifically proven that horses scare easily and attempt to flee in situations they deem dangerous. In my opinion, no amount of police training is going to override their nature completely. 

Not only this, their is often anti-police sentiment which leads to objects being thrown at the police and people verbally abusing them or trying to aggravate them. Whilst the police officers  don't always deserve this, they did sign up to be police officers and operate on the front line. The horses did not, yet they face a lot of the abuse themselves. I am sick and tired of seeing horses pelted with missiles in situations they did not ask to be in the first place.