Religion and cults are very close at their inner cores. Although religion may provide a place of unity and holiness, it can also be used in a wrong way. A way that easily can turn into cult-ish manerishms. It can be used to make you see things from their point of views, where they want you to see what they think you should see, and ignore the things they dont wish for you to tug onto. This may be described as a manipulating way to get what they want, which is very common in cult enviorments.

But if you take the word control, doesn't that suit both cults and religion? Religions, in most cases control your whole lifestyle. From your birth, to your death. In Islam, for example, they teach women of Shia and Sunni to cover up as an act of obedience to god. Every religion has once been a cult. Jesus and his 12 apostles were seen as a small, dangerous and radical jewish cult centrlisized around a charismatic leader by the Roman Empire. When the leader, Jesus, died and the movement survived, grew, and adapted to society the cult transformed to one of the biggest religions the world has known.

I get how my opponent may view the matter, but religion are as centralized around their leader as cults. And with your hypothetical case I might like to add that that sound very much like a few known religious movements. Jehovas Witnesses are some of those who comes to mind on the matter. There, members are strongly encouraged and expected to marry only within the baptized faith. Another one is Islam where they under more traditional and stricter views restrict or forbids marrying outside the faith completely. And within the first sentcae you made about a group telling you who to marry suits both cults and religion. Especially regarding the matter with same gender marriages. Endogamy, requirement to marry within one's own religion or social groups are in both cults and religions, thank you.

I dont really know how that argument is supported by anything you said, but that is something both religion and cults shares. Deep psycological, social, and emotional similarities because both structures often demand total devotion and treat departure as a profound threat.