Tell them bitcoin gives privacy, and allows them to be in custody of their funds without a third-party. No one have control over their bitcoin as long as they keep it in their noncustodial wallet. If they are still not convinced, leave them alone because the are skeptical people and you wouldn't be able to convince them. Let them invest in altcoins and you invest in bitcoin, in the long run they will see the difference for themselves. Experience is the best teacher.
If OP's friends care about privacy, decentralization then they won't care about altcoins, clearly what they want is just to find a high return investment. And for those who are only interested in profit, explaining the use cases and advantages of bitcoin is useless.
If I were the OP, I wouldn't waste time trying to convince or argue with them. Instead, I will let them experience the market themselves and after gaining experience, they will realize for themselves what are the best investments they should be interested in. Because everyone has different views, visions, thoughts and everyone has a big ego, so trying to convince others is not a wise idea. Instead, let them experience it for themselves to learn the most practical lessons.