You don't have to have a word-for-word statement from the passage for it to be an assertion of the author. The author does believe that Exxon is a villain.... look at the wording of the statement at the end of paragraph 2, "In an oil spill, such as the 1989 Exxon Valdez oil spill [] the villain goes without saying." The author is saying there that he doesn't have to outright say that Exxon is a villain, because it is so obvious it "goes without saying". That feels like a fairly strongly worded assertion.
Hope this helps!
Meaghan