Better not to make yourself that being mindful about on  where they will really be that investing because its their money after all and if you dont really like to have that kind of argument in between then it will be ideal on letting them out on where they will be that investing because its their own perspective and view. If they do able to experience up some loses then this is the moment or time that the will be having some realizations that it is more worth on investing into those projects which is on Bitcoin that gives out somewhat that security at least or having that less risks if we do speak about long term approach. If you do really like to put up some risks in involving into altcoins with having that proper risks management then let them be.

As for making up some arguments or explanation into your friend then i wont really be bothering myself on telling them.If you have told them about Bitcoin and they wont listen then just let them be on investing into altcoins because its their preference on doing so. Its normal that we will be spotting out into something that could bring out that much better profit opportunity in compared when investing to Btcoin. Each one of us will really be having that personal view on things on where we do really be able to put up our money on which in accordance in our assessment whether it could give out such potential profitability or not. So it will really be that situational into this aspect.