Why shoukd you define as legal or illegal. Just take a note, countries who adapted bitcoin have considered as legal and who are yet to adapt have not yet announced as illegal. It depends on the laws made by individuals. Its just the market competition between fiats and crypto currencies. When crypto stands up in the market, too many crisis do come hence it should not be considered as illegal. To be fact it aims to be legalised everywhere and is striving towards it.
very much depends on the policy of which country we are in, but basically bitcoin is legal, but many countries feel threatened by the emergence of digital currencies, because it has the potential to eliminate the dominance of existing currencies, so the status of bitcoin in various countries is still uncertain, this only a matter of business competition in the banking sector which is likely to be reduced by their money trees being replaced by bitcoin, because bitcoin offers convenience in all forms of payment and security.