Its a simple strawman that is being used to attack those showing support for Gaza.
The basic gist of all similar statements is along the lines of "somewhere else in the world, something worse is happening, so why don't you focus on that instead and let this thing happening in israel be burried?"
It's quite a powerful argument - thousands have been killed in Syria.
However the thing about Syria is that we all know what is happening there is wrong and we are all ciritical of it. Our government (that is the British government) is also critical of the Syrian regime and we support its criticism of the Syrian regime.