are the only truth
I don't know what this means.
same time say that you are humble
What you believe to be true about abstract concepts has nothing to do with being humble. Being humble is all about your views on the superiority of certain individuals not certain beliefs.
Being humble would mean admitting you can't possibly know for sure if you are right and opening yourself to the beliefs of others, doing otherwise is arrogance.
Being uncertain and being humble are two conditions unrelated to each other. Being open to other belief is a third condition unrelated to humility nor certainty. You can be certain, humble, and open.. uncertain, arrogant, and open.. certain, arrogant, unopen and any combination in between.
But it's like if I as a man one day decide to start wearing dresses ....
You are comparing physical conditions, with mental decisions. It doesn't matter what society around you is like. They can force you to do or not do something physically. but what you chose in your heart in the privacy of your own head is beyond their control. And it's an islamic belief that reward is proportionate to the effort. someone who have to go to great difficulty to preserve his religion (like, say a muslim during the spanish inquisitions) has a greater reward than one living in a supporting environment and both are good in their own way.
Say Hinduism is the truth, what free will does a Catholic Senator in the USA or a Muslim Imam in Egypt have to become Hindu if the choice just does not occur to them, Hinduism just doesn't even enter their minds. Therefore they could not have chosen to be Hindu. Where could they possibly have chosen to become Hindu if it did not occur to them?
Good point, but completely unrelated to the issue of humility.
I guess what you are trying to say is "what fault did a random guy born in the forests of Brazil and never heard of Islam do by never becoming a muslim? why would he punished when he was never presented with the choice?" And to answer that choice, I'll give you one verse and a short video.
^ From those we conclude that a muslim as an individual can not feel arrogantly superior to this hypothetical individual man. (Remember, being a muslim is not enough to guarantee heaven and avoid hell) So there's no problem of humbleness here.