There is also nothing wrong with trading or with interest. Some people are confusing interest with
Riba (closest translation is Usury). It is basically "unjust, exploitative gains made in trade or business", although Wikipedia is not the most accurate article but you can read about it here:
https://en.wikipedia.org/wiki/RibaYou're correct, this what Riba is. But if you're visit to a country where vast majority are Muslims and you said interest or Bitcoin is halal, they will criticize you and not want to hear what you're going to say. They have a thought where Bitcoin is haram because having no physical appearance and interest is always related to immoral, so you wouldn't able to win against them.
If I lend someone for $1,000 with 10% interest rate for the next 30 days which is he should pay back for $1,100, it's not Riba/Usury.
But if I lend someone for $1,000 with 10% interest rate for the next 30 days, but he can't pay back during 30 days and then I give punishment for overdue day(s) he need to pay +$50/day, this is Riba/Usury since there's no agreement for late payment.