okay, what i find a little frustrating about posts like this is the idea that you are somehow powerless against "all these takers" who are preying upon you (along with the other "givers").
this isn't fair. you see, i've been characterized by others as a "giver" as well. and yes, there are at times that folks (both friendship and romantic prospects) have sought me (or my time) and have been clingy, exhausting, and needy--perhaps characterized as "takers". and yes, these folks could certainly be drawn to the "giver" types.
BUT, it's simply unfair to explain this as "all your trouble". unfortunately, it's a lot more complicated, and as the "givers" it's always our responsibility to create healthy boundaries and expectations for ourselves.
first, there is seldom purely "takers" and purely "givers". it's not that simple. what one of you might describe as a "taking" relationship isn't to another. each couple develops what is right for them. and, in the absence of any objections or boundaries (ending the relationship, even) you are by default, participating. also, i would suggest that someone might define themselves as "generous and giving" by being generous with things that they value, but not really serving the relationship. it is human nature to be quick to acknowledge our own generosity and slow to acknowledge others' (especially in an unhappy relationship) but at the end of the day.
second, at some point, you are choosing this (unhappy or mismatched) relationship for yourself. and if that is okay for you, then i would say, that your real problem isn't because of the so-called "takers" preying upon you.
the REAL problem is that you have a broken picker--you are choosing the wrong kind of people for relationships and perhaps don't know how to identify what you want. you are possibly one of the folks who could really benefit from articulating the list of attributes that you are actually seeking (indirectly, the subject of this thread) so that you can recognize who it is you're looking for, rather than being charmed by other attributes that might be comely upon face value, but have no real merit in a mutually beneficial relationship.
and, at some point, you are electing to engage in a relationship with someone who is a "taker", by allowing this to continue. either you aren't addressing this matter in your relationship with communication and honesty, or you are ignoring the issue, hoping it will change.
or, you are failing to alter your expectation. but no one forces you into a relationship with a "taker".
while i can't say this is true when i was younger, i have gotten pretty good at identifying who shares my values and expectations for a relationship. if we aren't on the same page, then we aren't a good fit.
but for you to find yourself in a forced scenario with a "taker" just isn't possible. you even explain that "you had to get done wronged by him multiple times" before you rejected a friend. i don't know the circumstances, but at what point are you accepting that you have chosen to remain friends with him (up to the point that you said no more) and, by default, are also agreeing to the behavior?
while i think i understand what might have been the intention of the original statement that introduced this dialogue about the "takers" preying on the "givers", i think it's pretty dangerous for us to start blaming these so-called "takers" for the ills of our bad relationships.
further, i'm proof that "givers" can certainly attract other "givers", and aren't destined to a miserable life of women (or men) who are only takers, preying upon the unsuspecting "loving and generous folks" that are out to give.