As regards America, the people have got the Constitution and the views of the founding fathers to back up their right to own guns-
"A free people ought not only to be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government."- George Washington
"The strongest reason for people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government."- Thomas Jefferson
"Arms in the hands of citizens may be used at individual discretion in private self defense."- John Adams
"To preserve liberty, it is essential that the whole body of the people always possess arms, and be taught alike, especially when young, how to use them."- Richard Henry Lee
"The greatest danger to American freedom is a government that ignores the Constitution" -Thomas Jefferson
"The right of self defense is the first law of nature"- US judge St. George Tucker (1752-1827)
So the only grounds the US Govt could have for denying some people that right is by using the following quote to say that some people are NOT peaceable, for example if they've got criminal convictions and therefore shouldn't be legally allowed to own a gun.
"The Constitution shall never be construed to prevent the people of the United States who are peaceable citizens from keeping their own arms."
- Samuel Adams
The vast majority of the US people are peaceable, so I shouldn't think they need worry about having their guns taken away.