Yes they all are illegal, just like mangago...
The majority of the sites where you can read everything for free are illegal.
Korean government have been fighting pirating for years, the owners of Bamtoki have been arrested by the police and many authors have applauded that and promise to continue the fight so I wouldn't be surprised if Toonkor is the next prey.
It's is legal (they're the one who released the news about the arrest), the authors work for them and are paid by them. They're official "editors", that's why you have to pay to read there, because the author and people working on it need the money for their job just like us. Well there are many other companies not only L*zhin.
CAN ANYONE ON MANGAGO ENLIGHTEN US WHY WEBTOON.BAMTOKI.COM HAS BEEN SHUT DOWN ┗( T﹏T )┛ ┗( T﹏T )┛