Enquiries into this bloodbath will no doubt be whitewashed

Why?

One outcome for the people of Israel is an inevitable increase in their insecurity with no prospect of peace.

I think most believe there is no prospect of peace from Hamas, and their security has been maintained at the border.

Any protester who had actually managed to get through the fence would have had absolutely nowhere to go from there and could have been taken into custody

If the fence were breached there were tens of thousands ready to swarm in.
There are farming settlements within a mile. Previous incursions by tunnels and fence breaking have targeted any Jews within reach.

There was never the slightest need for the IDF to open fire.

That is what an enquiry would have to establish.
They may find that faced with large scale incursion there was no other way to protect the fence. Let's not pre-judge the outcome.

As things stand, nothing else can put the brakes on this brutal regime.

That is an extreme view of Israel.
It is run as a Western style liberal democracy with a vociferous opposition, free media, and regular elections.