Why is "From the River to the Sea" so divisive?

Moncrieff

Earlier this week, a Labour MP in the UK was suspended after he used a particular phrase that is igniting controversy: "From the River to the Sea".

It's been heard at protest marches but also during political discourse as the Israel/Hamas War continues.
But its history and meaning has been exploited on a number of sides. Scott Lucas, Professor of International Politics at the UCD Clinton Institute, explained its history and why it's become controversial.