What the New York Times regards as "killer" amendments on guns

To the New York Times, if you have ever had a mental illness, you should be banned for life from owning a gun.  How is that reasonable?  What incentives does that create for people to seek help?  As to concealed handgun permits, again, is their opposition to letting people carry concealed handguns across state lines reasonable?  Why are these considered killer amendments?

. . . That lobby has lined up several senators to do its bidding by offering amendments that will pose a real threat to the background-check bill. The worst — a huge priority of the N.R.A. — would require every state to honor the concealed-handgun permits of other states, overriding their own restrictions. That would allow a resident of Florida, where deliberately lax laws have given out such permits to hundreds of felons, to carry a concealed gun in New York or Connecticut, where the laws are much more strict and sane. 

If this amendment were to be attached to the background-check bill — and there may be enough votes to make that happen — the underlying bill would no longer be worth passing. 

Another potential killer amendment, sponsored by Lindsey Graham, Republican of South Carolina, would reverse current law and allow people who have been involuntarily committed to mental institutions to own guns, a ludicrous undermining of the background-check system. Only those who are found to be an “imminent danger” would be prevented from owning guns, even though that standard isn’t required in many states to commit people to institutions. . . .