[grandalf]

> The moment you take incentive (bitcoin) out of the equation, whole blockchain will lose its strength.

This assumes that the compute power of the miners who are left after the incentive is gone will not be sufficient to prevent attacks.

It also assumes that the miners who quit, whose hardware would seemingly be ripe for use in attacks, would have no other purpose to use it for, such as another cryptocurrency.

FWIW I'd also point out that I would not be surprised if a fork were to occur that prolonged the incentive. Consider the finite incentive something that was necessary to create the initial coordination among participants in Bitcoin, but once it reaches sufficient scale if continuing to have an incentive benefits the ecosystem then surely it will (by then).