Landlord is right in that it's unsafe to plug in and the circuits are likely not rated for it. I worked on many old buildings and often you'll have barely 2 circuits for the whole unit. Sure it might draw as much as a hair dryer, but a hair dryer alone maxes out a circuit. That's why the US code for example mandates a dedicated 20a circuit for bathrooms. Canadian one is behind in that regard in my opinion. Meanwhile in these old shitboxes you have your fridge on the same circuit as your living room, etc. Overloading circuits is a legitimate risk of fire, especially with older wiring and breakers that are basically never replaced when they trip and are in service for decades. Or the old oversized fuse/penny in the fuse trick.

It's not as easy as just slapping an ac unit in your window, the wiring needs to be updated.

Now I do think these people need air conditioning, absolutely. The government needs to step in and either force the landlord to pay for wiring upgrades (specifically dedicated circuits for window units, maybe panel upgrades to increase capacity, maybe service upgrades for entire buildings to accommodate the need) and/or subsidize the upgrade to some extent.

It's definitely not going to be a cheap fix though.