All shonen mangas are pro-life haha, it's generally dedicated to a teenage audience who needs a feeling of meaning by the pursuit of dreams, solidarity, friendship, internal growth and accomplishment.
All of that allow young people to develop a positive mindset to cope with life. If there was an acceptance of suicide in these adventures, it would risk to completely destroy all the magic view of life that a shonen manga brings.
What bothers me more are seinen mangas wich are anti-suicide as they are dedicated to an older audience and does not take place in a fairy and naive world.