Oh don't mind that, the president is just yelling at the TV again.

The person was quoting Trump. He tweeted that this morning.

If you start using tankers, you have to evacuate everyone from the area (in a larger area than their current evacuation cordon). It would mean all other on-site firefighting operations would have to stop.

Using aerial tankers would be unsafe (flying planes are very low altitudes through a city), and would result in a net reduction in firefighting efforts on scene.

Fire retardant might work, but is likely not readily on hand in an urban environment (and is really meant to prevent spread of fire, not to put a fire out).

Dumping actual water would be a bad idea both for the people and the structure, simply because dumping heavy things from high places is generally dangerous.

Yes. Potentially far, far worse. And people have absolutely died from using fire retardant delivered from air tankers.

These planes have to fly extremely close to the ground to deliver their payload (which is spread over an area far too large to be effective in this case anyway btw) and too often the plane can lose control, whether from sudden unweighting or the turbulence from the fire and crash. This can kill everyone on board and usually starts a new fire to boot.

Tankers are great at dropping water and fire retardant on trees, brush, and small structures.

Dropping tons of water on Notre Dame's roof would likely just expedite the collapse.

Donald trump just picks an idea that will sound like "common sense" to a lot of people. It makes sense in a simplistic kind of way, but is fundamentally flawed. But people get to feel angry that their ideas are not being taken seriously. And that the world is being ruined by stupid liberals who won't do the obvious thing. As if a fire chief in Paris has a duty to try out bad ideas just to protect the feelings of a random Twitter handle and his followers.