What do you guys expect? I mean one of the main princilpes of sikhism is about equality and not differentiating between castes but sadly this is definitely not followed by many sikhs today. In my opinion not only Sikhs but everyone should not believe in the caste system, it is mean and outdated. These "low-caste" ppl are not even considered sikh, I've heard the word "Adharmi" used for them. Furthermore I dont think anyone converting to christianity is anyone's business. Everyone has the freedom to practice the religion of their choice and besides isnt Sikhi all about One God anways?? I think you guys are forgetting that.
I dont think these missionaries should be using sikh words as mentioned earlier though but other than that its really not that big of a deal. There are other issues in this world bigger than this.