You are the one who introduced the DCA method, so you should know the risk as well. Also, if you are going to give him a loan so he can use it in the DCA method, isn’t it better if you just use it yourself? And you just said he is having some good turn up, then why would your friend still ask for a loan? If he really is and still asks, it means he is getting greedy or he is letting his emotions control him. Maybe that’s a sign you shouldn’t give a loan.
Investing requires having money that's secure and not intended for long-term use. If you don't have that, it's better not to invest. Especially since they aren't a hedge fund or VC with experience in managing investment funds. They simply listened to what the OP said and were tempted by the profit.
It's best not to lend money to someone who doesn't understand investing, or who only knows the profit without understanding the risk. DCA also has risks, as the market will always fluctuate. On the other hand, there must be a set amount of money allocated for a specific period of time. How would they get that if they were just borrowing?
Logically, it's better to use it for themselves. The OP wanted to motivate them, but they were attacked by the question. Instead, they could provide profits and repay their debts with those profits. It's better not to lend at all.