Is it ethical for advisors to automatically coauthor papers? I work in a field (Philosophy) where co-authorship is uncommon and advisors and grad students very seldomly co-author a paper. I've seen a lot of posts on Academia.se though about the ethics of co-authoring papers with mentors, such as this question.

My sense is that it must be somewhat common in the natural sciences for the head of the lab/dissertation advisor to be automatically added as a co-author to every paper that his or her graduate students produce. 

My questions are:


Is this really common, and if so, in which fields?
Is this really ethical? 


My view is that adding your name to something that you had no part in creating is just plagiarism: it's taking credit for the work of others. 

The opposite argument, that the work wouldn't have been possible without the PI's grant funding also cuts no ice. I wouldn't have been able to write my dissertation if my parents hadn't had sex, but that doesn't mean they should get credit as coauthoring my work. 

That's the way it seems to me, but maybe somebody from these fields can give us a better rationale for (what seems to be) the widespread practice.

Edit:
Another argument against the practice. Suppose I'm a billionaire who knows nothing about science, but I take it into my head that I want to be (regarded as) a famous scientist. Suppose I just spend billions of dollars to fund other people to do research. But, I ask each of those people to come and report to me for fifteen minutes ever week about what they've worked on, or discovered that week. Then, every time one of them finds a result, I demand that my name be added to the paper as a co-author, since we have "discussed" the work in progress and it is, after all, by my grace that the funds for the work have been provided. Suppose I just have hundreds of these postdocs, producing thousands of papers a year, all of which I am a coauthor for. 

Now ask yourself if I really deserve to be regarded as a famous scientist at all? It seems to me that I don't, because I haven't done any of the science--I haven't suggested any research methods, I haven't designed any experiments, I haven't collected any data, I haven't even helped junior researchers know the shape of the existing literature. You might regard my existence as good for science in some sense--you might think of me as a beneficial patron of the sciences. But you wouldn't think of me as a scientist, right? And you wouldn't think I deserved to be considered for a Nobel Prize, or membership in the American Academy of the Arts and Sciences, or whatever. If I demanded that I be given those awards because of the thousands and thousands of papers that I have coauthored, which have been cited tens of thousands of times, you would call me an idiot, right? We give those prizes for discovery, not for being rich. The same thing is true of tenure too. You shouldn't be able to buy your role as a tenured professor. You should have to prove that you, personally, are capable of making a serious contribution to your field. And of course you demonstrate that capability by publishing papers.

So when a prof is automatically added as a coauthor to a paper that he or she did not contribute to in any way except financially, then she is trying to buy a reputation as a scholar, or the other perks like tenure or membership in the AAAS that come with that reputation in just the same kind of way that the absurd billionaire is doing.
No, automatic co-authorship is not ethical – irrespectively of the discipline! 

The following is from the "DFG Proposals for Safeguarding Good Scientific Practice" (pp.82f, emphasis added), which, for instance, strictly forbids "automatic" co-authorships and gives a couple of common negative examples:


  Authors of an original scientific publication shall be all those, and only those, who have made significant contributions to the conception of studies or experiments, to the generation, analysis and interpretation of the data, and to preparing the manuscript, and who have consented to its publication, thereby assuming responsibility for it. [...]
  Therefore, the following contributions on their own are not sufficient to justify authorship:
  
  
  merely organisational responsibility for obtaining the funds for the research,
  providing standard investigation material,
  the training of staff in standard methods,
  merely technical work on data collection,
  merely technical support, such as only providing equipment or experimental animals,
  regularly providing datasets only,
  only reading the manuscript without substantial contributions to its content,
  directing an institution or working unit in which the publication originates
  
  
  Help of this kind can be acknowledged in footnotes or in the foreword.


In fact, DFG (the German Research Council) requires you to sign strict adherence to this ethical code on each and every grant proposal. Other funding agencies have similar regulations.