Ever since we are born into this world, our lives begin by being cared by others. We grow to realise, implicitly that people are essential. How could we comprehend any other possibility?
So we try to be friendly, often more than that is necessary or possible to be reciprocated as humans are different. Why do it then? Because it's convenient to think, to have more friends is to share good times with many, thereby meaning more happiness.
The danger of it is letting toxic people in. They will come, eventually. They always do. The trick is to recognise who are the ones causing the sort of drama which leaves you not feeling at the top of the world.
People who cause drama, need to be weeded out, ruthlessly. Those blissfully unaware of the damage it does to those around may perhaps deserve the benefit of a doubt, once. But just once. Life is too short to try to be nice towards those adding misery.
Having fewer friends who are more thoughtful and caring is not only energising, but also adds an immense amount of meaning to life. The value of a meaningful relationship is unmatched against a thousand casual friendships or a hundred one night stands.