Dontstarve_steam is damaged and can't be opened. You should move it to the trash.

There's a workaround by "whitelisting" it in Privacy & Security which can be found in System Settings. 

In Privacy & Security scroll down to the Security section and you should see a message saying the program was blocked from use because it is not from an identified developer.

Click on Open Anyway, enter the password, and you should have the option to click Open.