Surely you didn't mean to have what your wrote come across like it did - here is what you said:

"I think we should be cautious about these types of movies where "social action" is presented as the appropriate focus of Christianity.
...

These types of unbiblical involvements in the world system are fruitless: they don't win souls to Christ, which should be our focus. We should look for our true human "freedom" and racial/gender/wealth "equality" in Christ ONLY, which is promised to us in heaven. But not now!"

Matt

You imply working to right what is wrong in society is unbiblical  -

If we truly follow Christ we will have fruit in this world that manifests itself in loving our neighbor - Jesus said in Matt 5:16 "In the same way let your light shine before men, that they may see your good deeds and praise your Father in Heaven"

Paul wrote in  1 Cor 7:21 about if you are a slave and can gain your freedom you should do so

Proverbs 24:11 Rescue those being led away to death; hold back those staggering toward slaughter.  If you say "But we knew nothing about this", does not he who weighs the heart perceive it?"  

The call to social action is stated clearly in Isaiah 58:1-14 (from verse 58:6) "Is this not the kind of fasting I have chosen:  To loose the chains of injustice, and untie the cords of the yoke, to set the oppressed free and break every yoke?  Is it not to share your food with the hungry and to provide the poor wanderer with shelter - when you see the naked to clothe him and not to turn away from your own flesh and blood. 

Countless Millions of people have come to know Jesus as Lord because they saw Him manifested in people who were acting as His Hands and Feet providing food, shelter, clothing, medical treatment, ending injustice.  The call to social action is straight out of the Bible.  Romans 10:24 "Nobody should seek his own good, but the good of others"

William Wilberforce heard the Call from God.  He suffered terrible health - in the movie it is stated he had colitis which is just extremely painful (I know I have it) and made worse through stress.  He didn't use his ill health as a reason to quit trying.  Only through Christ Jesus did he have the strength to carry on year after year against all odds waging this fight.  Because of his willingness to give his life for Christ, God used him to help transform Western Civilization into a whole lot better place for a whole lot of people.  We are still reaping the good from the sowing he did.  He understood though, that when people truly follow Jesus societal conditions will change for the better.

I realize that we will not have perfect justice and no societal ills until the return of Jesus the King, but God clearly calls us to change the portion of the world were He puts us for the better to bring Him Glory. 

The focus of Christianity must always be Jesus but the practical manifestation of Christianity will always be improving people's lives because when we love one another, we help one another and make life better for one another.

Is God calling you to take some action that you are resisting and justifying your resistance by telling yourself you are not getting involved with a worldly system?

Just a note - "He taught that slaves should obey their masters, and that the run-away slave should be returned" is incorrect. Paul wanted run-away slaves to voluntarily return to their masters to show them the power and love of Jesus Christ.  Jewish law states in Deut 23:15 If a slave has taken refuge with you, do not hand him over to his master.  Let him live among you wherever he chooses.  Do not Oppress him.

Pepperpot