The expressing of emotion comes with a lot of side benefits: the other person becomes aware of your feelings (yes, people generally don’t know how you feel about something). They will respect your boundaries better.
You can tell they've never dealt with a person with narcissistic / sociopathic personality disorder. You express your emotions to them, all it does is provide them with a crystal clear signal of how to push your red buttons and believe me they will.
A lot of therapy is based on the assumption that "we're all the same" or "we all mean well" but it's simply not true. There's real scum out there.