It is very odd that this behavior exists at all.
My guess is that it comes from Google Calendar existing in it's current form before the integration with G+, which means that the public availability of invites has always been there, but the ability to mass invite a person has not (because details of a person has not been available)
As was said by +Andy Higgins
, this behaviour is precisely what you would expect from a Calendar in a business situation. What has happened, however, is the Google Calendar, long being used as a business solution (integrated through various means with desktop software), is now being made to work with the social media solution that is G+.
The problem, however, is that the bit that makes Google Calendar a good Business Calendar makes it a totally awefull social Calendar.
This leave Google with a bit of a problem. The natural, and apparently obviously, solution is to say "only allow invites from these Circles" to the Calendar. However, how will this affect current business use of the Calendar? as the Calendar is used by many business as their default Calendar, such integration could
mean a change to the security stream necessary for adding events to calendars.
Thus, you could end up in a situation where you need to have your Boss circled on G+ in order to be able to add business meetings from him in your business calendar (this used by way of clarification example
). I'm sure that none of us want to have to circle our co-workers, nor do we want to be forced to use G+ just to use their Calendar app at work.
What will need to happen, then, is that Google will need to offer several secure ways of adding events to the calendar, which is likely to be a bigger job that it may at first appear, because existing functionality must be maintained.
While in the short term it is easier for us to turn off
automatic adding of events to the Calendar, this is not a solution, something that Google has already acknowledged.
I don't know how Google is going to solve this particular problem, especially as the current philosophy of Google is for tighter integration between it's web platforms (for easier management, and of course, better stream-lining, and cost savings). Then again, that's why I don't work at Google.