My experience has been a bit different. There are always "parasites" - but for the most part, the people I have interacted with were mostly "symbionts" who gave as much as they received.
My biggest problems came from the "
Well Intentioned Dragons." These people ruined more ministry opportunities and drove more people from the church than all other causes combined. They got excited about baptism in Jesus name from a Bible Study I gave and then would promptly go home and send their families to hell. Thanks guys, but I was hoping to win your family to Christ as well...