Just from the manual itself, it seems Corps were created with a definitive positive and negative in mind.
I get that coupled with inflation, there may be a bug that is causing the cost to be way too high, and possibly makes it too strong of an ability to use against an opponent, however...
The majority of posts I've seen seem to be of the mind that this is intended to be beneficial only, and spread everywhere.
I really don't see this as the intent either. Even the basic manual seems to phrase it so that the downside of corporations can be considerable.
Like I said, not arguing a bug could exist, but I do think there is a major downside to the Corporations, that they were intended to be used carefully, and that placing them in opponents cities for a negative effect was also intended.
The strength of it, as opposed to their intent, can certainly be argued though.
some of the limits of spreading them everywhere exist already: competition between companies, foreign competition of companies with your companies, maintenance, inflation, potential espionage to courthouse, finite resources.
also, you can spread them everywhere, as long as they arent your own cities, and potentially you can do your best if you simply just plop one down in a friendly colony or vassal, and let them take on all the costs by them spreading it themselves.
so it's a bit of a double standard. and the fact that the AI isn't exploiting the demolition of a courthouse if you have corps while you can easily see the net effect of this against them is a bit unfair too.