should we put unbelievers to the sword?

Off with his head

On Judgement Day our attempts to be religious will testify against us.  They'll seek to gobble us up; so we need to defang them in this lifetime. 

A holy book may tell believers to compel unbelievers to believe, and to kill them if they refuse to believe.  Notwithstanding the the fact that you can't really force someone to believe something, believers may obediently drench whole empires in blood trying to fulfill the command.  And you know what God will say to them on Judgement Day?

He'll say, ‘How hard, exactly, did you work to make people believe before resorting to the sword?  How winsome did you make yourself?  Did you intoxicate the whole world with your kindness and generosity?  How much did you contribute to culture and architecture and science and wisdom and world peace and tolerance and community and laughter before you thought, “Enough of that.  These people won’t listen.  Let’s decapitate them”?  Did you go as far as you could possibly go before you picked up your sword?’

The answer, of course, will have to be no.  You can never go far enough.

God will continue: ‘So you had the effrontery to kill people who I created, who I made myself, because you found it too taxing to win them over with your goodness and reasonableness and creativity?’

The believers will be miffed.  ‘You said we could kill, Lord.’

‘I fixed an impossible precondition to your lust for violence.’

‘How were we to know?’

‘Didn't get the hint when I said that I am love?  When I said I am all-merciful?’

‘You tricked us, Lord.’

‘I tricked the evil in you to come out of hiding and show itself.’

That's the kind of conversation you'll hear on Judgement Day.

Is there a chance that you might be in need of mercy on that day?  If so, in the days leading up to that day, it's best to err on the side of mercy.  That's how you defang your religion.