If tomorrow Hindus or Sikhs start reciting Kalima, will we also accept them and treat them as friends?
So if a Hindu or Sikh professes his faith in Allah and Holy Prophet (SAW), you still won't consider him a Muslim, and he certainly won't be worthy of your friendship? What does a person have to do to earn his faith in your opinion and become worthy of being called your friends?
What if the Holy Prophet Muhammad (SAW) had adopted the same stance and rejected everyone who accepted Islam?
In my opinion, it would be absolutely delightful if a non-Muslim declares (without fear or coercion) that there's no God except Allah and Muhammad (SAW) is his messenger. Why would you get offended by this?