The inalienable right to the pursuit of happiness.

Those who are not looking for happiness are the most likely to find it, because those who are searching forget that the surest way to be happy is to seek happiness for others.

Did he really said that? There are roughly 3.5 million places on he Internet where someone attributes that quote to Martin Luther King Jr. On the other hand, I've yet to find anyone who gives a source for it.

Is it unfair to ask, on this Martin Luther King Day, if the quote is terribly profound? As is the case with Mother Teresa's remark about giving "until it hurts", we repeat this quote and we claim to believe it but we live our lives in a way that directly contradicts that claim.

I think that is no way to find happiness. I think we could correct the quote by having it read something like,

Those who are searching for happiness often forget that you cannot find happiness for yourself without also seeking happiness for others. 

You are not going to get something you don't pursue. What the famous quote says about liberty is also true of happiness, it is something to be taken not given.
Virtue is its own reward. We can say this and miss the point. Virtue is hard work; no one would pursue it if it wasn't worth having. If you spend your life in misery pursuing things you don't want thinking that you'll be rewarded for this, you'll end up miserable. And you'll deserve to be.

You'll also be a barrier to the happiness of others.

A sensible human once said, "If people knew how much ill-feeling unselfishness occasions, it would not be so often recommended from the pulpit"; and again, "She's the sort of woman who lives for others—you can always tell the others by their hunted expression." CS Lewis

Anything you deny yourself you will also tend to deny to others as well. No matter how well-meaning you try to be, you won't believe they are legitimately entitled to pursue happiness either.