Should we care as to who goes to Hell?

If, as Calvinism claims, the outcome of everyone's life is predetermined, why should they beg the lost to be reconciled to God. Their lip service to a command made useless by their false doctrine is idiotic...

If, on the other hand, the lost have an actual opportunity to be saved by the grace of God, then begging the lost to be reconciled becomes our heart-felt act of love...

 

Well, there's always this:

15 but sanctify in your hearts Christ as Lord: being ready always to give answer to every man that asketh you a reason concerning the hope that is in you, yet with meekness and fear: 1 Pet 3

The Lord sent me many such 'opportunities' back in the day.

 

...which begs the question, do 'slacking soulwinners' result in MORE people going to hell? ...

...do diligent soulwinners result in MORE people going to heaven?

 

It has nothing to do with Calvin. Predestination is very clearly taught in the Bible.
So, your question of why is actually directed at God himself.

Why does God tell His children to go and spread the gospel of reconciliation to the world when those who will be saved are already predetermined by God?

The simple answer for the servant of God is: Because my King tells me this is His means of saving those whom He has chosen.

Any deeper inquiry shows us that God keeps his reasons to Himself and doesn't tell us. But, here you are, Van, questioning God anyway. I encourage you, Van, keep asking God why. But don't say that it is Calvinists who made up predestination. They didn't. All they did was observe that God reveals this truth in the Bible. A truth you cannot deny without denying the Bible itself.