Someone can be both "likely to become a public charge" under the law (which is not yet in effect because three federal courts have ruled it unconstitutional) and also of great benefit to the country.

He's not an American, but Stephen Hawking, for example, was a "public charge" whose substantial medical bills were largely covered by the NHS[1] and the cost of his 24-hour nursing care was made possible through grants.

And while Hawking is an extreme example in both the cost of his care and his ability, a determination that someone is "likely to become a public charge" can apply to just about anyone who might find themselves in need of Medicare. An otherwise healthy 20-year-old with a family history of Parkinson's or Alzheimers. Or, to get even more dystopian, an otherwise healthy 20-year-old with a genetic marker for Parkinson's or Alzheimers. The cost of long term care for these diseases is astronomical but I'm certain there are many Parkinson's and Alzheimers patients that have made substantial contributions to society.

[1] https://www.theguardian.com/commentisfree/2017/aug/18/nhs-sc... (Written by Hawking himself)

[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1123440/

The law saying “likely to be a public charge” is already in effect and is decades old. The recent change that is currently blocked is only about the factors being considered when making that evaluation (specifically, usage of various types of government assistance).

Hawking and other successful people would also handily qualify for visas based on achievements.

Cost, governments are not benevolent entities.