OK I am an atheist
Why should I convert to christianity?
Good question. Examine the evidence, and if your conscience & investigation lead you to Christ, that would be neat.
And if you choose otherwise, I respect your choice.
The obvious reason would to so I could be saved from torment in hell, which I do not believe in. So that has no merit.
I empathize with your viewpoint. When I was an atheist, the argument from hell was not particularly compelling because I didnt subscribe (at that time) to the existence of such a place.
Having said that, however my disbelief (and yours) does not determine the factual existence or non-existence of hell.
IOW, given that you dont believe in hell -- that does not mean that hell does not exist.
So, if there is any chance that you might end up in hell (even though you dont believe in it), it would be worthwhile to investigate the evidence and make an informed choice (regarding the existence of the Christian God).
I am perfectly happy knowing that when I die I'm not going to be judged (fairly or not) as I do not believe in an afterlife
It is not clear to me how you can "know" this for a fact. You might believe this (above) to be the case, but how can you "know" this for a fact?
IOW, your statement sounds like you absolutely "know" that the Christian God does NOT exist, and hence hell does NOT exist.
How can you know these things as absolute facts?
I used to be an atheist. My search led me away from Atheism and to Christ (to the opposite conclusion from what you mention above). E.g., See
http://www.godsci.org/gs/chri/testimony/seek.html for a summary of my path from Atheism to Christ.
I ask what can I possibly gain from calling myself a christian? (other than the respect of christians, which I believe I already deserve)
As far as I can tell you dont gain anything of particular value by merely calling yourself a Christian.
However, if the Christian God is real, then truly commiting your life to him (becoming an adopted child of the Christian God, by choice) has eternal value. You will fulfill the eternal destiny that you were created for (to live in eternity in beauty & joy and in the presence/fellowship of others who rejoice in beauty and joy for eternity).
Cordially,
John