I have been with thousands of Hindu khatris /Arora, i never heard about it. I never see they marriage first cousin or same gotra. I have been close to mehta punjabi (khatri) community, they are totally against it and consider taboo. Some Arora people in past due it due to less education and low population or poverty. All arora community doesn't do it. Some individuals of the community do it, which is very less population - 10 in millions. Even Arora community against it and considers it taboo. In modern times, they considered it sin and taboo. I dindt know about sikh arora people, i know they even dindt do it. If anyone doing it from any community we are totally against it.