People do not generally believe a seat belt limits your liberty, but you're not exactly wrong either. But maybe in order to understand what they mean it's better to not play devil's advocate. So try an example like the NSA's mass surveillance. This was instituted under the pretext of keeping Americans safe. It was a temporary liberty people were willing to sacrifice for safety. But not only did find the pretext was wrong (no WMDs were found...) but we never were returned that liberty either, now were we?
That's the meaning. Or what people use it to mean. But if you try to tear down any saying it's not going to be hard to. Natural languages utility isn't in their precision, it's their flexibility. If you want precision, well I for one am not going to take all the time necessary to write this in a formal language like math and I'd doubt you'd have the patience for it either (who would?). So let's operate in good faith instead. It's far more convenient and far less taxing