In another word, everyone is selfish.
They may involve themselves in selfless activities, but you can be sure they do it to seek fulfillness within themselves in the grand scheme of things. Is donation an act of selflessness? It is selfish on a bigger scheme of things, as the activist RECEIVES joy by spreading the happiness. The selfless still got something going on them. Will the selfless give if it detriments their position? They may give their lives to save their loved ones, but they will still die happy because they’ll achieve something that benefits them in the grand scheme of things.
But to be fair, there are 2 sides of the coin: the good and the bad. The good selfish ones benefits society, but the bad ones consume it.