Two huge problems with Fascism. First is forced labor. This may not be a big problem in your towns, but it is a huge problem in captured towns as they have little pop to use.
Second is you have to have another anarchy and if not religious that is a huge hit at the point in time where you can least afford it.
A third problem is that it is an optional tech at a time where you have better techs to learn. Some of us do not research Nationalism, so that is two optional tech to research.
Just exactly when do you want to work on those techs and not work on say Steam, RP, Ind or the ToE?
Monarchy is an AA tech and is just fine for Alway War. Troops support becomes a lessor issue at this point in most games as you are starting to get quite large hopefully.
Corruption, I don't care about. I am only using the core for troops anyway, the rest are farms.