I am surprised that there are many 'sikhs' who do not believe in re-incarnation and they argue against it. The website sikh-philosophy.net is full of such people who claim themselves as being sikhs and yet deny this and many more concepts of Sikhi such as Naam jaap and others.
ਸਤਿਗੁਰਬਚਨਕਮਾਵਣੇਸਚਾਏਹੁਵੀਚਾਰੁ॥