From Real Life Villains Wiki

The Animal Rights Militia (ARM for short) is a faceless organization comprising of many radical animal rights groups working together in support of a shared ideology: what makes the ARM different from direct action groups such as the Animal Liberation Front (ALF), is that ARM members never take any precautions to prevent any casualties - in fact, many members believe in utilizing terrorism tactics, and for this reason, the movement is seen as much more dangerous.

Tactics utilized by those who follow ARM include (but are not limited to) arson, letter bombs, contanimation, death threats and vandalism - although these groups tend to target hunters, animal testing labs, and other obvious targets: for example one of the groups associated with ARM sent a letter-bomb to No. 10 Downing Street (the abode of the British Prime Minister) - this could easily qualify as attempted assassination and simply serves to further the group's infamy.

The philosophy of ARM is a simple but extreme one - simply put, the members of ARM do not care if they have to endanger human life in the pursuit of animal welfare, and are prepared to use far more aggressive tactics to further their goals.