Why the hindus RSS is spreading false lies about sikhism ?

I understand you're not talking about all Hindus or Hinduism in general, just this RSS. I know what you mean. I studied Hinduism for a while and found it an inclusive religion. Most Hindus see Sikhism, Jainism, Buddhism, Charvaka etc. as Dharmic. It honestly suprised me to see people like RSS viewing these other religions as bad or wrong, considering it is Hinduism which states, "Truth is one, the sages call it by many names".