Yes, it is important for Christians to stand against other religions in America, because these false religions lead people to eternal damnation in Hell.
Only Jesus saves!
Religious pluralism is a problem for Christianity that is based on the Holy Bible, because only Jesus Christ can provide eternal life. Other religions lead people away from eternal life.
Practically, if you want people to be saved, then would it be more effective to lead them to Christ with proliferation of other religions or diminishing of false religions?
In other words, effective Christian evangelism necessarily requires diminishing of other religions in American society. It is an active process that is required as a necessary part of Christian missions activity.
Allowing religious plurism is destructive to Christianity and Christian missions, because Christianity emphasizes salvation by Christ alone.
In other words, it is impossible to spread Christianity in a society that proliferates religious pluralism. Two are mutually exclusive.
In other words, obedience to the Great Commission requires downgrading of religious pluralism in society.
Evangelism is, in fact, an assault on religious pluralism.