A similar analogy that occurs to me is the justice system. Yes, there will be guilty criminals who walk free of a innocent-until-proven-guilty, trial-by-jury-of-your-peers justice system. The alternative is convincingly worse enough that we accept the false negatives and outliers of the system that protects us.

In this case, letting millions suffer in poverty with real effects of poor healthcare (instead of investing in preventative care), restricted access to better opportunities for themselves and their children seems thoroughly worse than accepting the outlier "parasites."

I am of the belief that given the foundations of Maslow's hierarchy and a real education, many of those "parasites" with limited opportunities can be changed into people who feel they have a chance and pursue "self actualization." Poverty is a vicious cycle; it's hard to be ambitious in a "i want to change the world" way when you have no choice but to take whatever you can to support your family on minimum wage.

I agree completely that instead of throwing money at administrative peripheral problems like eliminating any parasitism, we should address the root problem.

Overall, people living in poverty do not have the same opportunities as the wealthy. Given the same opportunities there is no reason that they would not pursue the same "worthier" career aspirations. The assumption that poor people are parasites is the most colossal example of Fundamental Attribution Error[1] I can think of.

[1] https://en.wikipedia.org/wiki/Fundamental_attribution_error