I thought that "forced" marriage requires demonstrable coercion by some other person, for example in the case of a kidnapped bride, or of a parent over a minor. Thus, it would point to absence of consent.

Yet isn't it so that an adult of sound mind always acts with free will in regard to the actions of oneself, and that this is a core element of traditional Catholic belief?

Yes I believe this is true.
It's hard to say you were "forced" when you controlled your own body to go through the marriage ceremony, say the words of the vows, etc.

The only way you could be "forced" is through violence, OR through threat of violence. Some third party would have had to apply extreme pressure on you.

Feeling like "there is no other way", "feeling trapped", doing it for your family's sake, doing it for economic reasons, or any other remote "forcing" doesn't count as forcing.

Forcing is a literal shotgun wedding, threat of violence, basically you didn't want to but were literally FORCED to.

Princess Peach marrying Bowser to save the lives of all the cute mushrooms in the Mushroom Kingdom would be an invalid marriage, due to a constant threat of violence, which never leaves the background. (nevermind the fact that Bowser is a fire-breathing dinosaur; a cross-species marriage would always be invalid). 

But the woman in (the movie) Titanic marrying the jerk rich guy to save her family from financial ruin and embarrassment? That would be a valid marriage if she went through with it. It's up to her free will. The movie was realistic in that it was HER choice to reject him or accept him for the sake of her family's social standing. Look how easy it was for her to reject him and have a fling with Leonardo Di Caprio. That portrayal WAS realistic. That just proves it wasn't real FORCE. Just strong encouragement.

Anyone have a location and Mass times for the KS resistance chapel - Fr Brocard?  For those who want to break from St Marys

Corner of Hwy 63 and Crystal Springs Road, in Emmett. Silver building with St. Jospeh statue above the red door.
Sun: 7:30 Low Mass and 10 AM high Mass
M, TU, FR, SAT: 9 AM
TH: 6 PM
WED: 11 AM

And the biggest problem is that most people DON'T have a priest available to answer important questions.

You can always make an appointment with the priest. 

There a couple traditional Catholic groups that are having get togethers for young people. Try that. Maybe someone can give you the info.