Read
Solver's review of Corporations, he explains how they work and how he thinks State Property is even nerved too much because you can't use corporations anymore.
Building and spreading corporations is very viable, but it needs be done right and only if your economy can handle it. I guess a lot of people just haven't got it under control as of yet.
Exactly, I dunno where weimingshi got the idea that "The designers clearly stated that corporation is there to screw your opponents."
It is supposed to be a whole new aspect of gameplay, not simply a different form of military conquest.
Basically they did with corporations what they hadn't dared do with religions. Now some corporations can't simply coexist: you must remove one to place others. Corporation is very close to religion, although its not a clone and I realize there are differences.
With religion there was an incentive to convert to the other guy's state religion because you got +culture in your cities and +1

with the option of another +1

from a temple and additional +3

for 1/3 of your cities with mosques or equivalents.
In the same way, corporations should give benefits in their branch cities that give those civs reason to take your corporations. In game as in real life, the countries that would accept corporations are those that can pay for the benefits - aka cottage economies, whilst specialists and workshop economies simply couldn't afford it even if they liked the.
Also corporations require as many of a resource as possible, so they would most likely be more beneficial to the already rich countries (as in real life).
For the less developed countries with only a few of the resources required, they may get more benefit from state property and instead simply selling off their raw materials to other rich states for them to use in corporations (again as in real life).
So again your black&white statement that corporations are simply a hammer to beat down on any and every opponent is stupid, especially so because you need open borders to spread them [hence they tend to be more your friends than enemies].
The decision of whether to choose SP or stay in an open market is much more complicated than simply "who owns the HQ".
Having said all this, the biggest benefit of course goes to the person with the HQ who like a religious shrine gets +

per branch.
... again I'm simply bewildered that you think corporations are a negative thing and that you simply found the corporation but don't ever spread to your own cities only to others and in so doing, you destroy them.