There are many who don't believe God will punish people.

I would suggest that those people read this passage.  If God did this to punish the generation coming out of Egypt, what makes you think God won't do that now?

Hebrews 3:16-19(NKJV)

For who, having heard, rebelled? Indeed, was it not all who came out of Egypt, led by Moses? 

Now with whom was He angry forty years? Was it not with those who sinned, whose corpses fell in the wilderness? 

And to whom did He swear that they would not enter His rest, but to those who did not obey? 

So we see that they could not enter in because of unbelief.