Jesus talks about how the kingdom of heaven is like a man who catches many fish with his team of fisherman and than put the good fish into containers and through the bad fish away. To me the fish symbol the religiously faithful.
Some Christians use their religion as an excuse to be a good person, they build hospitals, do volunteer medical procedures, run sandwich drives for the homeless, tutor disabled students in Matthew or English, visit lonely widows at old folks homes, encourage and help their friends quit bad habits like drinking or smoking and work extra hard to please their employees at their job. These are the good religious ideologies that Jesus talked about.
Other people use their religion to vilify those who have non traditional attitudes to marry, humiliate spend thrifts who waste money, mock people who are weak or insecure, judge fat people or poor people, avoid socializing with old people or disabled people, make xenophobic comments about people from our religions, oppose welfare for unemployed people and try to impose their own morals on those who have a different lifestyle or slander those who interpret religion in a different way than themselves such as worshiping on Saturday instead of Sunday. These are the evil religious people.
So good fish are good religious ideologies and bad fish are bad religious ideologies, you chose whether you want to love or hate others in the name of God.