I think it is only illegal if there is a law that makes unregulated market illegal. The crypto market in my country is still largely unregulated but the people are free to use and trade any cryptocurrency from both local and international exchanges. Some countries have already imposed their own regulation to curbe some illegal activities and protect their people financially.
It seems like what you have told a lot has happened to the developing world, there are still many who have not received developments about crypto so it is too late to make regulations that can regulate it. but indeed, if there is no regulation, this is clearly illegal. because crypto users need definite protection, so that it doesn't become chaotic in the future.
How could we say simply non-regulation marketplace is illegal? Decentralized market contains bitcoin, ethereum and many altcoins, will you say these coins are illegal and you are not using too? I am not sure what is your problem and why saying that it is illegal.
There are bad activities happen on blackmarket we can consider that alone illegal. We should not say everything as illegal.
The guy above is only confuse , based on what i read he only means that crypto needs regulation so that it can be more acceptable and will look more legal on the public . this is what i also think when crypto is already fully regulated just like fiats where every people in the world will not doubt on crypto anymore but for now cryptos are not yet regulated but this does not mean that they are already illegal .