This is based off of money being fungible. Qualifying for this money for cancer screenings means they have more general funds to dedicate to abortion. This means that, without govt funding, PP would have to make a choice of what to do with their general funds: Fund medical services and birth control, or fund abortion.
What this law does, such as the similarl aws passed in a few states (including Indiana) doesn't eliminate cancer screening funding. It just means you can't do it at Planned Parenthood.
I have absolutely no problem with cutting off funding to PP.