I had to laugh at this post. Anyway let me show you that the passage you have quoted has absolutely nothing to do with (a) demons -- not even mentioned here, nor (b) debate -- also not mentioned here. As others have already pointed out, Christians cannot be possessed by demons.
The whole chapter is about the bondage of the Old Covenant vs the freedom of the New Covenant, and goes back to the Judaizers who had come into these churches.
24 Which things are an allegory: for these are the two covenants; the one from the mount Sinai [the Old Covenant], which gendereth to bondage, which is Agar.[Hagar] 25For this Agar is mount Sinai in Arabia, and answereth to Jerusalem which now is, and is in bondage with her children. 26 But Jerusalem which is above is free, [the New Jerusalem corresponding to the New Covenant] which is the mother of us all.
So what was Paul telling the Galatians in this particular passage (vv 12-16) which is somewhat of a digression?
PAUL DID NOT BELIEVE THEY HAD HURT HIM
12 Brethren, I beseech you, be as I am; for I am as ye are: ye have not injured me at all.
PAUL REFERRED TO A BODILY DISABILITY OR INFIRMITY
13 Ye know how through infirmity of the flesh I preached the gospel unto you at the first.
HIS DISABILITY WAS A TEST FOR THE GALATIANS
14 And my temptation [test] which was in my flesh ye despised not, nor rejected; but received me as an angel of God, even as Christ Jesus.
HIS DISABILITY COULD HAVE BEEN POOR EYESIGHT
15 Where is then the blessedness ye spake of? for I bear you record, that, if it had been possible, ye would have plucked out your own eyes, and have given them to me.
PAUL WAS NOT THEIR ENEMY BECAUSE HE SPOKE THE TRUTH
16 Am I therefore become your enemy, because I tell you the truth?