I don't quite understand the reasoning for "unconditional love" or the urge to give it, IMO some people are not deserving of love. There are people in this world who will take and take and take from you and will keep taking from you until you have no more to give. Why waste your time and energy on people that do nothing but drain you (what is referred to as "psychic vampires") when you could be spending all that love and care on someone who actually deserves it?
Throwing energy away in the hopes that one might "get better" or that they might change, is one of the main reasons women stay with mentally/physically/emotionally abusive husbands- and that hope is the reason why some physically die at their hands. Whether they physically die or not is irrelevant, they have been killed or injured metally/emotionally, why put up with it?
If you have children, then yes, there is a certain give and take but then you yourself have taken on that responsibility, and the type of person they become is largely a result of your own doing and influence. Even then, when they reach adulthood if for some reason they become a "taker" with little care how it affects you, one shouldn't feel guilty if they feel the urge to "cut them-off" so to speak or actually do it. Just the fact of someone doing that may give them the wakeup call to change or they may just move on to the next "victim" to suck dry- it's up to them, but ultimately it's up to you what you allow happen to you.