The constitution specifically describes how it can be amended. Is it purposefully difficult to change so spur of the moment ideas can't influence it? Yes. But except for a couple sections, it's not designed to be written in stone.
In fact, excepting the Bill of Rights, the constitution was amended on average once every 11 years between 1795 and 1992. I'm not really sure why we've stopped for almost 20 years now. If people are really so bothered by constitutional limitations, change the thing.
The reason we haven't amended it is because many parts have had a very stretched and loose interpretation applied that let's government get around it's restraint.
The whole point of the constitution was to restrain the federal government. Anything that is not specifically stated as the authority of the Federal gov. is reserved for the states.
If you could change the constitution on a whim then we would essentially have a democracy which is rule of the mob.
When it says the right of the People to keep and bear arms shall not be infringed. It means just that. Any gun controlled measures should be up to the people of the specific states.
The whole point of having seperate states is that if you don't like how something is done in your state, it is:
A) easier to have an influence in your state capitol than it is in Washington DC.
B) it is much more practical to move to another state than to leave the country.
I don't understand why people want to the Federal government to have such broad powers. Isn't it better if things are different from state to state so that people have more choice on how they want to live?