There are those who believe legislation is necessary to prevent further school shootings by banning certain guns, or gun accessories, or, now, adults not yet 21 from buying certain firearms.
Gun rights advocates oppose any legislation that restricts ownership or purchase rights on the grounds that, to borrow a cliché, if you give gun control advocates an inch, they will take a mile. In this, they have something in common with abortion rights advocates, which have opposed any restrictions on abortion or government abortion funding for the exact same reason — that having succeeded in some restrictions, anti-abortion activists will push for more restrictions.
In a democracy it’s not clear that anything can be done about that. The theory obviously is that if you’re successful at restrictions on gun rights or abortion rights, advocates of those positions, having gotten one legislative success, will push for others. Those people also will push politicians on their side to push further.
Abortion rights opponents would say the difference between these two issues is that, they believe, every abortion ends a human life. Gun rights opponents would say that guns can end human life too, but guns do not shoot themselves.
A libertarian might say: Don’t like abortion? Don’t have one. Don’t like guns? Don’t buy one. But of course government’s main role now is to allow interest groups to take away things from their opponents.