Isn't proprietary software more reliable and more feature-rich?
The reliability of free software compares very favourably with that of proprietary software, as it is demonstrated by their extensive usage in the Internet infrastructure (a domain where reliability is a key feature). In addition, the number of code readers and testing volunteers assures an early and exhaustive bug detection and correction.
The key point lies elsewhere. When a software claims to assure democracy in a group of users, it is absolutely necessary that the source code be open and accessible to all. Indeed, it is the only way to assure that the software will indeed perform what it claims to, and that it does not contain exceptions, hidden traps and loopholes through which malevolent people would modify its behaviour (by manipulating ballots, destroying work, dissolving working groups, retaining information transmission ... the imagination of power confiscators is infinite).
It is therefore because their source code is open that we chose to use free software.
In addition, relying upon a free software is a means to re-use a considerable validated code base, legally.