From what I have read, and what I would also argue, buddhism makes the point that increasing your own happiness it is not a selfish thing because when you are happy those around you are more prone to also become happy. Like if you are happy and smile at someone and then it makes them happy.

So while maybe it could be argued becoming happy is selfish, actually being happy is not selfish. But then again becoming anything is selfish, I think the point is what happens after the point of becoming that thing. There is a lot of this logic in buddhism, which is why more importance is usually given to your volition for doing something than what it actually is your doing (think karma).

guylhem and blissofbeing both make very good points here. We can take into consideration the motivation behind the wish to be happy. It reminds me of a story I read while studying. I'm going to paraphrase here so please forgive any mistakes.

There was a man traveling down a road while it was raining. He came across a statue of Lord Buddha. He thought to himself, "The Buddha is getting all wet, that is not right. I shall cover his head so he doesn't get wet". He took off his shoe and put it over the Buddha's head.

Now, in those days (and even today in many parts of Asia) the act of putting something from your feet onto a Buddha's head is very disgraceful. In Thailand people don't even let their toes point at a statue of Buddha. Many people would think that man did something very wrong. However, his motivation was to protect Buddha and that single act was the eventual cause for himself to become a Buddha.

I am no expert and am just repeating what I have read elsewhere. Hopefully I did not mess the story up to bad and someone will still benefit.

Here's the story you're referring to: http://www.bodhitales.org/the-buddha-statue.php

What about when your selfishness is at a cost to others?

So for instance, fracking, or unethical medical testing, or massive layoffs, or hostile takeovers, or private paramilitaries and physical coercion.

So many example - I don't know if there is a generic answer!

But let's take them one by one.

Physical coercion is always wrong - it has a direct cost on others.

Layoffs are fine - no one has a right to work. Hostile takeover - ownership right are respected so that's ok. Fracking is an edge case - a negative externality if people already lived in a place and expected no such new industry would show up - so in that case, at a direct cost - and it becomes a bad thing.

If however similar or identical industries were already in place, yet people decided to move in, it's freedom - and it's fine.

Medical testing - I guess that would depend on what you mean by unethical. I'm sorry I can't answer for that one, expect by default a "direct cost" if you mean people entered medical testing while not being told the whole truth if laws requiring the whole truth to be disclosed exist, or in their absence if they were lied to. That's because it's just like cheating in a contract.

I hope this helps.

+1'ing you anyway since it's an interesting questioning about limit cases (and flipping the bird to the downvoters)