stoic

I'm going to have to disagree vehemently with your thesis. Weakness is a state, not an ethical behavioral descriptor. The state comes from exhaustion, overexertion, disability, or lack of conditioning. Altruism and kindness fundamentally require more effort and energy than apathy, cynicism, and selfishness.

Expecting kindness in return for one's expression of kindness is balancing on a razor's edge. On one hand, it is reasonably to treat others how you would like to be treated, on the other, it is a fact that not all will reciprocate. Building expectation on this reciprocation and depending on it for one's sense of happiness and well-being is like doing that balancing act with a backpack full of rocks; even if one balances successfully, the extra weight is going to lead to getting cut.

Depending on this reciprocation for one's happiness is also unfair both to one's self and to those that they behave kind to. It puts more strain on the interpersonal relationships because they are not able to read minds and know exactly the level of reciprocation expected. It also is unfair to one's self because it avoids the emotional exercise necessary to grow and be self-sufficient as well as leading to one being constantly in a state of reaction, rather than action.

It takes more strength to practice kindness and altruism while maintaining one's own well-being. Additionally, allowing others to take advantage of one's kindness is also not weakness but a lack of respect for and investment in one's self, and sometimes an act of self-harm. Saying "no" when one does not wish to do something or have the energy to share is an exercise in kindness and respect to one's self. Not associating with those that routinely attempt to take advantage and manipulate is also.