Without quoting directly from the email correspondence I had with them after they left RF;
1) Associating with apostates was cautioned against.
2) Putting brothers and sisters at risk by exposing them was cautioned against.
Unity and the risk of endangerment were the key thrusts of the discussion.
You may or may not see RF as much of a threat to either unity of JWs, or to putting people at other countries at risk, but the nature of the internet means that contact is somewhat faceless (any person can parade as anything, but be something else) and international.
I completely disagree with the ruling, but obviously I am not a JW, so that isn't important from their point of view. But I initiated email contact with them afterwards to try and understand the intent behind the ruling, and the above 2 points were re-iterated. Whether you believe those are the actual reasons, or whether you agree with them is up to each individual. For the record, I am skeptical on both counts, although I think it's quite possible that the people who left RF were sincere enough. My issues are more with the ruling body, since this smacks more of censorship and is a pretty classical method of information control. But I'm a cynical atheist anyway.
I wish they were still here. I like chatting with JWs, most of the time.