It was negligence and I reckon everyone can agree that the Lightning network is not for everyone. Avoid it if you are a person who is not smart enough to operate it.
I don't there is going to be a lot of people that are able to use it - we talked about having a network fast enough for real-life transactions and micropayments, with low fees, got it, but it's pretty hard to use and I doubt it'll ever grow big enough for it to be adopted by the BTC community, and be used for payments in the real world.
As for the 4 BTC loss, it's just FUD, and since the network is so new and pretty hard to use it's recommended that most people just ignore it unless they have a deep understanding of BTC.