This was and still is pretty frustrating. Microsoft sets a default value which doesn't seem to be used that much in businesses. So how do you deactivate this?
1. Go to:
"C:\Program Files\Common Files\microsoft shared\Web Server Extensions\15\TEMPLATE\LAYOUTS"
2. Search for a file named "AclInv.aspx"
3. Open that file and search for "id="chkSendEmailv15""
4. Change the value of "Checked" to "false"
Problem solved.