It is considered "reasonable" to restrict 2A rights when the "greater good" is served. Law abiding citizens are told that it is in their best interest if they are closely monitored when purchasing firearms, licensed to do so, registration, fees, etc. since these "reasonable infringements" will somehow lower the number of guns in the hands of those who would use them with ill intent.
The justification for this is that we have a crime problem. Some of that crime is committed with a firearm. And the crime seems to only be getting worse. Ergo "reasonably restrictions" on firearms, while doing nothing to lower actual crime, will lower the number of crimes that utilize a specific tool.
It is also understood that kids exposed to violent movies & video games, and music that glorifies the thug culture has a major impact on their ability to discern between right and wrong. Many, if not most, of the crimes committed with firearms are inner-city residents who grew up in single parent families with pervasive drug use and sex in their households.
Shouldn't we start "reasonably restricting" the 1st Amendment and not allow Hollywood to make violent movies? Isn't it in the best interest for the general safety that we forbid hip-hop artists from glorifying the thuggish lifestyle? Sure, it goes against Freedom of Speech but we're talking the "greater good" here. It's reasonable to ask artists to not glorify a culture that is so damaging to our society.
We can "reasonably restrict" the 4th amendment too. By allowing police officers the ability to enter a house without a warrant, we could make it harder for parents to use drugs in front of their kids, especially if they know at any many the cops might show up.
Of course, the 6th amendment is perfect for restriction. It's very reasonable to allow people to accuse others without their identity being known to the accused. By "reasonably restricting" the 6th, we can get more people to turn in their neighbors without them worrying about retaliation.
Come to think about it, we don't need the Bill of Rights at all. We cannot feel safe if we are held to the antiquated ideas of individual liberty since that would allow others to do things we may not like.