This is on Less Wrong, a website devoted to rationality. You'll notice several times in the article he is clearly addressing a rationality-focused audience. For instance:

Without a magical deity to give you purpose, though, you'll have to find out for yourself what drives you.

He's writing for atheists. Telling an atheist "in order to be happy you need to get religion" is like telling a recovering alcoholic "in order to fall asleep you need to have a few drinks."

Instead of a recovering alcoholic, perhaps a teetotaler or other person sober on principle would be a better comparison. I've never believed gods could exist or had religion, and thoughts otherwise wouldn't tempt me.

You may be right. I chose alcoholic because suggesting they try drinking to solve one problem will cause other problems for them. If I were to try attending church in order to make myself happy, I would find myself 1) tortured by the inanity of everything that goes on there and 2) pained by the experience of behaving outwardly in a way that conflicts with my values.

However, there are also plenty of people who were raised religious who are now atheists. I've met many of them who have the same toxic relationship with religion that an alcoholic has with alcohol.

I share your views of religion. I also feel pretty much the same way if compelled to fake extroversion and attend, say, a fancy dinner reception. In the eyes of the article author, it is fine to dismiss religion while extroversion is to be coveted. I assume this to be because he is himself an extrovert atheist and can't imagine other people being happy in another way.

That's one of the entire problems with atheism: without a higher power to give your life purpose, it can be very difficult to suffer through yet another day on this earth full of such suffering and sorrow.

Nihilism has a similar issue.

It's icky.

And it is better to worship a deity that at the very least created "this earth full of such suffering and sorrow" if it isn't actively controlling it depending on your view of the deity's role in the world?

As for purpose it isn't that hard to have one; it can be as simple as to having a little happiness and trying to make the world around you just a tiny bit better rather than worse.

There is also no reason why for most people days should be things in general to "suffer through".

That's one of the problems with religiosity: you can't imagine a way to find meaning in the world without fooling yourself.

Or like telling a diabetic he needs an insulin pump.

Within a given country religious believers seem to be happier (based on many surveys) but I don't think you can suddenly choose to believe when you don't. On the other hand basically secular countries seem to have higher average happiness levels than fundamentalist ones.