Why does the narrator object to a sea trip?

The narrator says that he objects strongly to the sea trip because, while a sea trip can have health benefits if it is going to be prolonged for a month, "for a week, it is wicked."
The narrator elaborates on this comment, stating that on the first day of the trip you feel "that you are going to enjoy yourself," but by Tuesday, seasickness has set in to the extent that "you wish you hadn't come." This seasickness continues for the following three days. The next day, you are finally able to sip a little beef tea and sit above deck; the day after that, eventually, the suffering sailor is able "to walk about again, and take solid food." Unfortunately, by the time the sailor is beginning to feel well again, the week has elapsed and it is time to return home, just as the sailor is coming to enjoy the experience. Effectively, the narrator is saying that a sea trip takes a week to get used to; going on a sea trip for a week only is just enough time to spend several days feeling horribly seasick.