I think saying this was just "gesture" is wrong. It wasn't just an 'empty building' it was the chemical weapon factories and storage facilities. By destroying theme, Assad is without chemical weapons and it will cost him many millions to build it up again.
It kind of was to be fair, it needed to be done. But us, France and the US gave fair warning about the strikes and the Russian and Syrian Military will have vacated the area.
We need to send a message to not just Assad but to every other despot or potential despot that chemical weapons are crossing the line.
We need to also send a message to Assad and Russia that we are not completely passive.
This was the right level of action, targeted at chemical weapons infrastructure, to make said point without any major influence on the conflicts outcome or risk of escalation.