I just don't follow your logic there. Surely being busy is good for the success of the business. I'm sure any IF passenger who's looked after by Stena would look very favourably on Stena for getting them to where they're going.
A ferry operating at capacity isn’t necessarily a pleasant place to be, and that’s an experience people will remember regardless of the circumstances. Short term Stena make a few quid, granted, but that’s it. Nobody really wins out of situations like this, unless they were sailing with empty vessels anyway. Trust me, they weren’t. In any case many passengers only travel once or twice a year. They are having to turn away freight customers that may travel multiple times a day, every day. Those customers will be far from happy and are having to search out alternative travel arrangements. Not all freight is booked far in advance after all! Holyhead is down 16km of freight space no matter what way you look at it.
There’s also the pressure being put on Stenas call centre and customer service teams as well of course.