It no longer means anything in the world we have today. In the physical sense, there is basically nothing left to threaten the weakest, meekest or disease-ridden. Take the lion. The male lion can only maintain his pride as long as he's the strongest. The one most capable of protecting his lionesses and cubs. As soon as there is any sign of weakness, his throne is relinquished to the new strongest male and so on.
'The circle of life', to use a line from that corny Disney film.
Now if you're the weakest in society, you might not have a pride of lionesses, but you're still able to survive. There are prescriptions, treatments and cures for pretty much any of the things that can inflict a person. When did it become 'survival of the person with the best medical care'? To top it all off, they can then pass on their tainted DNA to their children. It's perverting natural selection for their selfish need to 'protect' their bloodline.
A mans' worth is now based either through fame, money or being physically attractive. Sure, it's good to have those attributes, but that doesn't measure any of the attributes you should truly be gauged on. Strength of character, the ability to think, the ability to empathise or strive forwards are a true measure of self-worth. I think it's the society we live in which has perverted the meaning of 'the fittest'.
Maybe we need to have a gladiatorial test of a man's strength, intelligence and drive to prove their worth as a prized catch. A similar thing would have to be devised for women, too. Then there would be a ranking system that would rate a person. Just as you have a credit rating, you'd have an eligibility or 'fittest' rating. It could be that if the rating was too low, you were no longer able to pass on your DNA.
Take Gattaca, one of my favourite films. The basic story revolves around a fixation of a man's worth by their DNA. Their future was determined by their strength of DNA which would determine what kind of role they were eligible for and who they could socialise with. The film concludes with a man, that despite having weak DNA, becomes a 'DNA elite' through subterfuge and strength of character. He is able to exceed all expectations despite being ranked weak within this society.
There's a quote that I think is brilliant:
'I never saved anything for the swim back'
His strength of character was such that he was so determined to reach his goal that he'd put everything on the line to succeed. Now that is a persons' worth that needs to exceed his lifetime.
So in conclusion, it's not that we save people who are weak, it's that the weak of character are able to continue their bloodline, destroying future generations in the process. The ability to procreate should be a privilege rather than a right. I think anyone who is willing to push their limits beyond what they should be capable of is worthy. Anyone who strives for a better future is something we should preserve. You can always do far more if you don't save anything for the swim back.