That could've been caused by the OP not uninstalling the program correctly or totally unrelated program errors. In that thread, the OP never mentioned losing ANY data, or even confirmed that Avira was the cause.
As I've seen many of the same threads you're referring to, I know what's been reported. If you can't come up with some proof that these quality, free programs (avira, avast, ccleaner, malwarebytes...etc) cause any harm, then you need to stop posting your disinformation. These programs are spoken very highly of throughout the forum, and help many more users than you know. This forum is here to spread knowledge and facts, not personal bias'.