The we could... quote was from the article and refers to the dear readers without presuming to know what they think - it's an exhortation.

Stock markets behave mostly irrationally in the short term (see Random Walk Down Wall Street), but that doesn't mean you shouldn't attempt to ignore the irrationality and get a little closer to the objective truth - in this case by valuing companies based on what they earn and could earn, not what someone else paid for them or might pay for them.

Depends what you're after I guess - if you are trying to make lots of money in a few days/weeks/years with borrowed money, you'd absolutely have to attempt to predict the irrationality of the market or go bust. On a long time scale with money which is not borrowed/required, you can afford to take a longer view based on profits.