For him this is about destroying any oversight which might put him in jail. His "partners" from the extreme right want to use it to annex the occupied territories without giving citizenship to 3M Palestinians.
Essentially parties that are part of current coalition tend to be regarded as "job factories" and supreme court interferes with it. So they are not happy.
Also they want to fire attorney general (also judicial advisor to government ) which manages criminal case against prime minister and in general tries to prevent unlawful laws from passing. Firing her given conflict of interest is currently "unreasonable"
And if we are talking about new justices. One of the next planned laws is the one that gives to government ability to pick justices of their choosing
There is no transition period. I agree that the clause is too subjective. But there is a lot of law resting on it, law regarding matters like corruption and the rights of minorities that are about to be swept away by this unilateral change. That's de-stabilising in a self-reinforcing way.
For one, with something resembling consensus.
> If the knesset passed a law saying that in 1 year the reasonability clause would be removed, would you be perfectly okay with that?
You'd look at the rulings the Court has made on the basis of reasonability that deserve codification.
What the Knesset is doing now is a constitutional overhaul. Unfortunately, Israel lacks a written constitution, so the mechanism for amendment is unclear. That said, if you consider this as a razor-thin majority making major constitutional changes, the instability and de-legitimisation that causes makes sense. (Constitutional systems require supermajorities for amendments for a reason.)