Besides of the health issues, Walter was working for a car wash company at the beginning of the first season and his pregnant wife was trying to get financial help from his ex-girlfriend who became millionaire thanks to an old scientific research of Walter White...

First question people ask is, is it ok for Walter White to cook meth for earning what he already deserves? It's the easy part of the question of Breaking Bad.

Walter White started cooking by blackmailing Jessie, one of his old students. (remember another student of him who disrespected and made fun about Walter when he was cleaning a car) From the first episode to the end of 4th season, Walter White has fucked Jessie's life up. He made many manipulations in Jessie's life to have Jessie work for him.

Hard part of the question starts here, is it ok for a teacher suffering from cancer to destroy one of his student's life for earning money?

To me, the answer is absolutely no. But I see that many people who enjoy how Walter White became a tough guy, think Jessie already lives what he deserves as a young punk.