I am a tenant, but in this instance, the OP, the landlord, is completely right. I have insurance on the contents of my rental property, but not over the electrical items supplied by the landlord for which they have their own insurance. They have to have them be safe- and if other people mess about with them, then they are breaking the terms of that insurance/may not be able to claim. Stripping the plug back off an integrally wired appliance which is 10 years old is a completely stupid thing to do and if it then burned the house down, it may be the insurance would be invalidated (or not, it's unclear, but that's why you shouldn't do it).
I don't know why the OP is getting a hard time here, the best thing about being a renter is that when the electrics blow, you tell the landlord and they have to fix it.
Increasingly landlords are providing fewer appliances for this reason, ours doesn't provide a washing machine now, and also rental insurance increasingly specifies that you need to have tested your appliances- we cannot use unPAT-tested heaters in our house, for example, without invalidating the insurance.
This is not a moral issue, or one about competence, it's about legal responsibility in the light of insurance!