If it is really stuck, cutting it out isn't that bad really, particularly on a stem. Seat post is more painful to cut out.

Realize you CAN put more force on a frame than it can take. I've bent frames trying to gorilla out a stuck stem or seat post. I have made a jig to hold the fork crown (carefully) in my bench vise, then put a long steel bar through the stem clamp (you WILL bend aluminum handlebars). I've gotten several out that way. Kroil for the win, PB Blaster is a joke. I've had panto'd stems where the stem was worth as much as the frame. So cutting it out was not a good option.

As a chemical engineer, I will NEVER recommend lye. First, it is dangerous. Secondly, it will destroy the paint. Forget it.