The security issue is that by default it is easy to accidentally make it so that any user can see and edit every other user's data. The one Meteor project I wo

The security issue is that by default it is easy to accidentally make it so that any user can see and edit every other user's data. The one Meteor project I worked on at scale we specifically wrote integration tests to try to read and write other user's data just to make sure we didn't have a hole open up. Because we did have a whole open up and we learned from our mistake. Part of the problem of Meteor is that it is "magic" in a lot of ways. Because so many things are so easy, when something doesn't work the way you want (like there is a performance issue) it is often difficult to figure out.