Because the rainforest is important in regulating global temperature and oxygen production, much more so than the (probable) temperate climate forests you are from.
You are living in a post destruction area, with new forests planted to supplement the destruction that was there before. Most of these forests aren't more than 70 years old, that's about when we finally made an effort to fix how badly we totally fucked up and why people needed clean air to not die from lung cancer (among other things). The loss of biodiversity, air quality, etc. already occurred. You are a survivor. What's more, your survival was in part supported by the air quality of other virgin forests further away from you that weren't yet cut down. But now that they are being cut down, there's less left to support you.
In short, you're asking yourself why you shouldn't shoot yourself in the foot again, because you managed to survive the first shot and it looks to you like it healed just fine (it didn't).
You are living in a post destruction area, with new forests planted to supplement the destruction that was there before. Most of these forests aren't more than 70 years old, that's about when we finally made an effort to fix how badly we totally fucked up and why people needed clean air to not die from lung cancer (among other things). The loss of biodiversity, air quality, etc. already occurred. You are a survivor. What's more, your survival was in part supported by the air quality of other virgin forests further away from you that weren't yet cut down. But now that they are being cut down, there's less left to support you.
In short, you're asking yourself why you shouldn't shoot yourself in the foot again, because you managed to survive the first shot and it looks to you like it healed just fine (it didn't).