Horses often come to us looking for attention. They have been taught to act in a domesticated and even submissive way. Perhaps they invented the idea of selfies before humans did! It possibly did not occur to them what situations of great harm and distress they would enter into as a result, having to bear men in heavy armour hoisted onto their backs, and to trample through landscapes of churned up mud and slaughtered bodies, human and animal.
Not all medieval attitudes towards animals were caring and patient by any means. At an early stage, women as well as men realised the extra leverage over their neighbours could be gained by saddling a horse and fitting themselves out with swords, spears and regular violent training.
We may sometimes be inclined to sympathise, as when an invading army has better resources and equipment. The Iceni led by Boadicea (Boudicca) had only local knowledge as their advantage over the empire-building Romans. Both sides were pagans, so we can’t hide behind loyalties to a Christian tradition to explain why we would side with one or the other.
Presumably it is just the romance of seeing a vulnerable yet brave underdog militia up, against a drilled and remorseless invader which makes us pleased to see a stirring statue of Boudicca in her chariot on the London embankment. Romance favours heroism, without much in the way of challenging self-awareness to question the means that are employed to win the day. Faith in the Lord Jesus who died for love of enemies is dimmed.