Is membership in the Catholic Church assurance of salvation?
Do bad-will Catholics choose hell instead of serving God?
I do not believe there are or ever will be any bad-will Catholics in heaven.
No, membership in the Catholic Church is not necessarily assurance of salvation. There are Catholics that do not persevere in the state of sanctifying grace and damn themselves at the end. Actually, even if one strives to be a good Catholic, there is still not such assurance.
There cannot bad willed Catholics in Heaven, only Catholics in state of grace.
The fact that one is baptized a Catholic and professes the Catholic religion is proof that God is giving one the special grace necessary for salvation. There is a vast majority of souls out there that have not that privilege. As far as how God chooses the predestinate souls, nobody really knows. Theologians agree that it is NOT because of merit that God chooses His elect and love some souls more than other.
There are certain souls, the Elect, who will infallibly be saved (they will be given the grace of final perseverance) but it is also true that God does not predestinate any soul to Hell (that is the Calvinist thinking). Among the Elect, are children who die shortly after being baptized, and adults who, by divine grace, not only can observe the commandments, but actually do so and obtain the gift of final perseverance.
In sum, if someone goes to Heaven is only because of God's grace. If someone goes to Hell is only his own fault.
While God loves all men, He has a special love for the elect and infallibly ensures their salvation. However, God does not command the reprobate to do the impossible. Although the call becomes efficacious for the elect and not for the reprobate because of God’s eternal decree, this does not mean that God gave no grace to the reprobate to enable them to respond.
Thus, in God’s plan of predestination, the reprobation of some is preordained for the good of the elect, and this for the greater good of the whole.