If your argument rests on your reader’s imagination, and you don’t care to elaborate when your readers don’t demonstrate that imagination, then yes, it is a failing of your argument. You can’t just say, “Well, if you don’t understand that’s not my problem,” unless you are saying, “Look, I’m pretty sure I’ve got a good idea here but I don’t know how to articulate it.” The point of the comic, if I understand, was that they took literal quotations and replaced ‘guns’ with ‘ballistic missiles’. Not being able to do the same with ‘free speech’ does make it different.
If you want to argue that overreach for freedoms is better than underreach, using Singapore doesn’t feel like ‘picking on someone your own size’. Singapore is internationally renowned for outlawing chewing gum, everyone knows they balance the good of society (as they see it) higher than personal freedom. What actual western democracies that have free speech and freedom of religion but don’t hold them as absolutely as the US does? My observation is that the US is closer to being a police state than Germany or France is, despite those countries banning certain kinds of hateful speech entirely.
And while saying that the entire system of US laws is invalid would be too far, I stand by my statement that Citizens United, Hobby Lobby, and the thinking they represent, are totally deserving of ridicule.