Man Gives Away £3 Million

Money Can't Buy Happiness, So Man Gives Away Every Penny of His £3 Million Fortune, article.
The man says:
"Money is counterproductive – it prevents happiness to come."

If that is so, isn't it a nasty thing to do to others to give them money?

It's a complex thing. The best answer I've found so far is that if your inner hurt makes you addicted to material things, you will be unhappy whether you have them or not. And if you have healed that inner hurt, you will be happy, whether you have things or not.
Giving away your money handles a symptom, not the cause. It might help you deal with the cause, but you can deal with the cause without dealing with symptoms.