==We can form a union when we need to form a union.==
In my 35 years of life, it has become harder to start a union, so it isn't out of the question that it becomes harder and harder to start a union when software engineers "need to". There's no guarantee that what exists today will exist tomorrow.
==Do people actually think that software engineering is going to become a job that isn't skilled, and isn't sought after?==
I'm not sure why you would be so sure it wouldn't. Are the software engineers of today truly that different from the machinists of yesterday?
If you believe in the free market, then it is elementary that more people will flood into these careers which will lower the wages and diminish the bargaining power of existing software engineers.
If your argument about it being elementary for people to flood into the career were true, then why have far older and desirable professions like law and medicine continued to be incredibly well paying?
Software is hard, humans have a hard time doing hard things, that's why we get paid more.