I don't know where you are coming out with this "killing business."
What is your problem? You do not like the word "kiling"? OK, change it for "eliminating". The meaning does not change - in the area of family immigration this bill proposes to eliminate all family immigration except for what they call here "nuclear family" - spouses and minor children (+ some quota on parents).
Next, notice that I did not express any negative or positive feelings or thoughts about the nature of this bill - just stated what it is planned.
Concerning youe emoitions on the subject, we all understand that state and individual interests differ, and sometimes substantially. That is why, in addition to this bill provisions, GC holder has to wait for years before being able to bring a spouse, while spouses on H4 cannot work, while B visas for relatives of immigrants are rutinely refused in some countries etc.
Immigration law is inheritantly not fair - because it is aimed for protection of people already "in" from those who are "out" and whant "in".
Now, when society becomes reach enough, it can allow itself to care a bit not only about economic profit but also humanitarian values. The degree to which the society is willing to forgo some profit in exchange for "feeling good about itself" and making their disadvantaged members feeling good is a very difficult problem..
By not allowing new citizens to bring their relatives the country discriminates agains them compared to "old" citizens - who were born here, and thus have all their family network in place..
Specifically about parents. If you look at the immigration system in other developed countries, they do not welcome adult siblings and children, but ALL of them provide citizens with a possiblity to brong their parents, though some demand the proof that a parent is lonely and economivcally dependent fro the petitioneer. Why do you think it is so? Probably because traditional human culture assumes some depts with respect to our parents and abandonment them in the old age is considered immoral im majority of the cultures? And thus the law which nocompasses some moral values, not only short-term economic profit, follows that principle?
I would agree though that those who bring parents should support them themselves, and not try to put the burden on the state (and as far as I understand it is enforced in US till large extent by asking petitioneers t sign the affidavit of support).