No and Yes. The answer depends on the consequences OF COURSE.
While someone like “donald trump”, for example, obtains its own personal happiness by dropping bombs on school children in other countries, then I think it seeking out its own happiness would be best not done.
However, if someone else, for example, obtains its own personal happiness by writing a book about how everyone as One can and will live in a universal Peace together, then I think it seeking out its own happiness would be best done.
So, in what exact context or examples were you thinking about here when you asked 'your questio?
Here is another prime example of how adult human beings ‘tried’ their hardest to “justify” their selfish and greedy wants and desires.
Look, “acltalls”, it is very simple and easy, if what you do makes you happy but abuses absolutely anything, then you can not justify you seeking out of your own personal happiness in absolutely any way in Life. If, however, what you do, which makes you happy, does not abuse absolutely anything, then 'that doing is justified, absolutely. And, if what you do, which makes you happy, also creates happiness in others, and/or is helping in creating a better world for absolutely everyone, then please, by all means, keep on ‘doing that’, as ‘that’ is exactly what is good and Right, in Life, and what others or everyone wants and desires anyway.
Hopefully you are now seeing more clearly and have gained a better understanding here.
Now, why did you write your question here as though if ALWAYS seeking one’s own happiness leads to the unhappiness of others for, exactly?
Any thing and every thing that helps in the creation of universal World Peace for everyone.
What people also personally get, besides their own personal happiness, is a sense of True achievement and True satisfaction, because they are ‘now’ finally doing and achieving what aligns with their natural True purpose in Life. When you human beings are doing ‘that’, which you all instinctively KNOW aligns with what is Truly good and Right, in Life.