The phrase 'dragoon into' implies a person is pressured or unwilling, giving a negative feeling. He felt upset after being dragooned into agreeing to the unfair deal.
Pro Tip 2/3
Power Dynamics
Usually someone in a position of authority or power 'dragoons' someone less powerful into something. The employees were dragooned into working late by their boss.
Pro Tip 3/3
Against Will
'Dragoon into' is used when someone does something against their will or without their full agreement. Martha was dragooned into hosting the event, although she wasn't comfortable with public speaking.