yes you can. Because it will likely be decades before the environment kills people but you can save a life today. Oh, don't drive that ambulance to go pick someone up and rescue them, it pollutes! Where as other solutions may exist for the environment in the future.

Here's another. Maybe no one should go hiking/camping/mountain climbing because the few that need to be rescued generally require cars/helicopters the burn fossil fuels to come to their aid, not to mention all the fossil fuels used to get them to their camp/hike/climb site and all the materials for their gear, all for "entertainment".

Also, you yourself are likely a net negative on the environment. Do you have an obligation to kill yourself?