I want to spend more time stabbing and shooting, and less time climbing radio towers. How do I do this?

Use a mod like Schwartz Mod Compilation.

This will unlock the second island, remove the Fog of War and allow you to purchase all the guns from the beginning of the game, even the Special guns.

This leaves very little reason to climb the towers in the first place seeing as the FoW is removed all over. Remember to revert back to the original files you replaced installing the mod when you want to go Multiplayer.

I don't know of any way to skip activating the radio towers, but there is a method to skip climbing them that I used a lot: just hang glide to the top of them.

For example, the glider located at X:654.9 Y:694.0 can reach most of the radio towers in the Northeast.

Their are some trainers that will teleport you to the towers with a press of a button. just make sure that you match the versions. i find that game copy world works the best. http://www.gamecopyworld.com/games/pc_far_cry_3.shtml. ow and you should not have to install any thing.