Matthew 10:16 Look, I am sending you out among wolves. So be as shrewd as snakes and as harmless as doves.
This says to me that as Christians we are to be harmless... and kind... but we don't have to be pushovers. We are allowed to be aware when we are being taken advantage of and we don't have to stand for that. We are to stand up and take notice, pay attention. We are actually suppose to be wise enough to protect ourselves.
Verse 14 says that if any household or town refuses to welcome you or listen to your message, shake the dust from your feet and leave. Our part is to be kind... to spread God's word... to tell others about how much God loves them... our part isn't to make them accept...it is to make sure they know..what others do with the information we give them is their responsibility.
As Christians we are to spread God's word and be kind and loving, gentle. But we don't have to take on the responsibility of others. We leave that part for them. We plant the seed and then let them choose to accept the seed. If someone comes to us and ask us to help that seed grow then that is exactly what we do. We are to be kind and loving and gentle to others...but we don't have to sit back and be taken advantage of because of our kindness... we can protect ourselves from harm.