Perhaps the main reason it bothers, is becaue there are laws against killing animals, and even just causing them discomfort. Muslims have a bad habit of ignoring US laws, and proceeding right along with their contradictory Islamic law, which they place above US law.
These people have no respect for the US Constitution, which forbids what they are doing on Eid al Adha, and a number of other things. (rape, slavery, misogyny, wife beating, pedophilia, etc). They are supremacists, who believe their Islamic law is supreme above all else. Not in America >>>
US Constituiotn - Article 6, Clause 2 - the Supremacy Clause
"This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land; and the Judges in every State shall be bound thereby, any thing in the Constitution or Laws of any State to the Contrary notwithstanding."