If your hands just won't grab that fabric and rip, try pulling a thread. If you make a small snip into the fabric and separate one thread, you can pull it out of the fabric. You need to work carefully so as not to break the thread, pulling a little then flattening the gathers. The pulled thread will create a line in the fabric that is completely straight as it is the line made by one straight piece of the grain. Sometimes I will cut as I go to shorten the distance of the pull or if the thread breaks, you will need to cut up to the broken piece in order to pick it up again.
Really, though, ripping is easier.