Adam Engst, writing for TidBITS:

In a move reminiscent of how Greenpeace harangued Apple for the PR value, MoveOn.org even sent out email encouraging people to sign a petition asking Apple to modify how Siri works, claiming that Siri “won’t tell you where you can get an abortion or even emergency contraception — instead she’ll promote anti-abortion pregnancy ‘crisis’ centers.” MoveOn went on to say, “When a user asked her why she is anti-abortion, she replied, ‘I just am.’” Oh, please.

Search engines are only as accurate and capable as the data they have to work with. (And despite seeming like magic from the future, for all intents and purposes Siri is just a search engine.) Google doesn't have a perfect algorithm for telling the difference between a vapid, spammy page about green tea weight loss and an actual article on the health benefits of green tea. Both look similarly relevant, in that they both contain a similar set of search terms—it's the context that makes one spam and the other scholarship.

If you ask Siri for "abortion clinics" and its (her?) data set doesn't use that word, then Siri can't answer your question. From its perspective, there is no such thing as an "abortion clinic", though "Planned Parenthood", "birth control", or "family planning" might exist, depending on your location and what clinics in your area call themselves. And if you asked Siri a different question, like "what is abortion", you'd get a different answer because you'd be searching within a different data set.

That said it's not impossible for a search engine to have an agenda. For instance, if Google detects a query for a local business name (e.g. "longman and eagle chicago") they now always promote their own local listings at the top of the page over competitors like Yelp, even if Yelp's pages are (objectively) older and more authoritative. But that takes work, and Google benefits by selling ads on those place pages. Apple doesn't benefit by hiding abortion clinics in Siri's search results.