WHO WON'T OBAMA ALLOW INTO AMERICA?

Brit State Media:

The US has lifted a 22-year immigration ban which has stopped anyone with HIV/Aids from entering the country.
President Obama said the ban was not compatible with US plans to be a leader in the fight against the disease.
The new rules come into force on Monday and the US plans to host a bi-annual global HIV/Aids summit for the first time in 2012.

This may sound callous, but why would we (Americans) allow immigrants entry who possess a deadly disease?