In Gintama the Movie: Be Forever Yorozuya (Yorozuya yo Eien Nare), why would Gin need to go to the future first? He was infected by the White Plague during the Joui war, so why would the future Gin need to have him sent to the future first to kill the plagued future Gin instead of just send him to the past and prevent the plague from spreading in the first place?

In Gintama the Movie: Be Forever Yorozuya (Yorozuya yo Eien Nare), why did Gin need to go to the future first? 

He was infected by the White Plague during the Joui war, so why did the future Gin call him to the future to kill the plagued future Gin instead of just sending him to the past and preventing the plague from spreading in the first place?

In Gintama the Movie: Be Forever Yorozuya (Yorozuya yo eien nare), why would Gin need to go to the future first? He was infected by the White Plague during the Joui war, so why would the future Gin need to have him sent to the future first to kill the plagued future Gin instead of just send him to the past and prevent the plague from spreading in the first place?

In Gintama the Movie: Be Forever Yorozuya (Yorozuya yo Eien Nare), why would Gin need to go to the future first? He was infected by the White Plague during the Joui war, so why would the future Gin need to have him sent to the future first to kill the plagued future Gin instead of just send him to the past and prevent the plague from spreading in the first place?