Maybe if you'd give subsistence to everyone (basic income for example) and let people produce in exchange for "more", the system would still be viable.

And do you have reasons to believe that would be so -- besides "maybe"?

No, that's why I'd like to see it tried. Nordic countries seems to be headed in that direction, we'll see how it goes.

Well, until their toilet clogged and stayed clogged because most plumbers became painters and the rest just went fishing. And until they got sick and found out that the line to see one of the few doctors left is a couple of months. And until the buses stopped running because being a bus mechanic is not such a great job and there are not enough guys who are willing to do it just for fun...

One possibility is too find a new equilibrium where the least attractive a job is, the better the advantages for doing it (since people would be ready to pay more to have it done at your place).

I would be fine with giving unproductive persons incentives so they become productive

In money or bullets?

You forgot the second part :

But then you have the question at how much incentive is ethically justified.

This is already how it works. And In a perfect capitalistic society, you have a choice between working or starving (except if someone is willing to help you), this is not much better than bullets.

I would go for less incentives that in our current society personally.