I don't think it's religion, personally, because in Christianity for instance you see the pro-lifers and the people at the border protesting to give refuge to Honduran asylum-seekers in accordance with the teachings of Jesus and they often seem to have essentially no common ground, frankly. On a personal level they do, but on a political level, nah.
Ah but I'm not arguing that this dispute is religious in nature or that religious people all agree (the bible has nothing to say on the topic of mass immigration anyway, AFAIK).
Rather that the people protesting for or against something because of their religious views are much less likely to suddenly change those views or crumble in the face of pressure from opposing activists. They have some sort of concrete belief system that they've thought about and are invested in - it doesn't have to make sense, but they aren't going to turn around and say, "ok ok I promise I won't be pro-life anymore" because some angry Google engineers tweeted that they must hate women's rights. Their views are more robustly grounded than that.
