Hi Keltoi
Under your defenition of christianity it might be simple. But other Christian denominations disagree with some of the things you listed as fundamental, which was the whole point that brother Al Habeshi was trying to make in the first place.
I agree that it is probably quite difficult to refute Christianity, in the sense Al Habeshi is indicating in his OP.
And the reason may be that the Bible (and therefore the interpretation of Christians of it) is much less prescriptive and much more open to interpretation than the Qu'ran is.
I see in this forum, how much confusion that causes in Muslims, and how it is perceived to be a weakness.
Compared to the Qu'ran that may be ... the Qu'ran is much clearer (not totally unambigious in some areas, I don't think, but generally much more defined than the Bible is) in what the do's and dont's are.
We have said it a hundred times in this forum - but
that is not how the Bible is meant to be read.
Strangely I find the openness of the Bible a real strength - in the sense that
it causes me to read, ponder, compare, discuss, read again, pray over, read again, pray some more ... (you get the idea

)
I do not just
follow the book, I also need to
look within myself, I need to
listen to my own conscience, I need to listen to
God's spirit within me. It is much more than just following an instruction manual!
As a consequence of Christians doing all the above, we come to have so many denominations.
Again, I don't see that to be a weakness. In the past as well as now, there have been people saying 'I don't agree with you on such-and-such ... I think it is so-and-so' ...
But as Keltoi so nicely points out, our differences are not as important as the basic premise of the Christian faith, which most denominations agree with (and those who don't are very much on the fringe of the Christian religion, if indeed still part of it ...)
The fundamental Christian doctrine is quite simple really.
We believe in one God the Father Almighty, Maker of heaven and earth, and of all things visible and invisible.
And in one Lord Jesus Christ, the only-begotten Son of God, begotten of the Father before all worlds, God of God, Light of Light, Very God of Very God, begotten, not made, being of one substance with the Father by whom all things were made; who for us men, and for our salvation, came down from heaven, and was incarnate by the Holy Spirit of the Virgin Mary, and was made man, and was crucified also for us under Pontius Pilate. He suffered and was buried, and the third day he rose again according to the Scriptures, and ascended into heaven, and sitteth on the right hand of the Father. And he shall come again with glory to judge both the quick and the dead, whose kingdom shall have no end.
The fundamental Christian doctrine is easily recognized, and those who do not follow the fundamental doctrine are easily recognized.
With regards to wishing to refute Christianity - why should that be so important in the first place?
How about 'To you your religion, to me mine'?
Peace