“Why are some religious Jews against Israel?” Some Jews come from the Erev Rav that left Egypt together with authentic Bnai Yisroel.
Over time, the Erev Rav intermingled with klaal yisroel. It became impossible to know who has roots in the Erev Rav and who is from the Shvatim. But on some occasions the Erev Rav rears its ugly head, specifically when it comes to Eretz Yisroel.
The Erev Rav did not have a chelek in EY (which was divided to shvotim only). Since the Erev Rav have no connection with EY, they try to discourage other yidden from maintaining the love and deep rooted inheritance they have with EY.
That is how we can tell who is from the Erev Rav – so it is really a brocha, when some Jews are against Israel, their mask is removed and they show us that they are Erev Rav. Only then can we can know who is an impostor in our midst.