It's somewhat hard to tell intentions but that seems a fair interpretation of at least some elements of the film
I think the filmmakers knew it was a challenge to make John remain sympathetic given his actions so they maybe intentionally made the crowd so supportive, kind of overdoing it to get the audience to acknowledge the absurdness and yet also be supportive themselves (and I think this worked). It seemed like a lot of the crowd anger was real and yet it was still a crazy response to a crazy situation (the crowd wouldn't have wanted to be one of the hostages). Certainly the news media is just in it for their own benefit and Frank seems correct when he claims the crowd doesn't really care about him.
The hostages laughing at John's joke about killing one came after they had been stressed for a long time and also partly from relief that they knew he wouldn't actually do it.