This was the cause of a heated discussion here a few months ago.
Back then, when I was looking for references on the pros and cons, I found out an interesting take on this matter here RSpec 3.5 has been released!
The official recommendation of the Rails team and the RSpec core team is to write request specs instead. Request specs allow you to focus on a single controller action, but unlike controller tests involve the router, the middleware stack, and both rack requests and responses. This adds realism to the test that you are writing, and helps avoid many of the issues that are common in controller specs. In Rails 5, request specs are significantly faster than either request or controller specs were in rails 4, thanks to the work by Eileen Uchitelle1 of the Rails Committer Team.
Even though this is a quote from Rspec, the part where it said that the Rails team recommend request specs caught my attention. As @Betsy said, I also agree that a strong defaut would make much sense and avoid lots of WTFs from new (and also experienced) Rails developers.