If Trip didn't think he was doing anything wrong, why did he feel the need to lie about what he was doing?
I think that he understood that the Vissians would not condone his actions. That didn't make them wrong. When Rosa Parks refused to give up her seat on the bus, she was defying laws, traditions, culture... were her actions wrong?
As easy as it is to blame the Vissian engineer and his wife, we have every reason to believe that their views on cogenitors are the norm among their culture. It seems unfair to blame them for simply being true to their cultural upbringing.
Their treatment of the cogenitor was so utterly hateful, she killed herself just so that she could bring it to an end. Excuse them for this if you must, but you must also excuse humans who whipped slaves for daring to run away, fought against giving women the right to vote, and threw gay people in the slammer for what they did in the privacy of their own bedrooms: they were acting within the parameters of their culture as well.