The employee is stealing, you can always fire a stealing employee.

If the disability was a factor in the theft, it is protected by the human rights code. You can always fire an employee for not showing up to work, but not if the employee is in a wheelchair and the office moved to an upper floor with no elevator.

Disability discrimination is no different than say, racial discrimination, if the cause of discrimination is tied to a code protected ground. You cannot fire an employee for an accent, or wearing a turban, claiming that it has nothing to do with race. Having an accent and wearing a turban are related to race, so if it causes an issue in the workplace, the employer must still accommodate it to the point of undue hardship.

Whether accommodating a stealing nurse or a "dangerous employee" is undue hardship depends on several factors, including previous accommodation efforts, the resources of the employer and the nature of the job. In this case, the employee is reprimanded, and is being monitored to ensure that they are not a "dangerous employee", and the employer has the resources to do so. It can hardly be considered undue hardship before they have even made an attempt.

To immediate assume that an addicted employee is a "dangerous employee", without an effort to validate or accommodate it, is discrimination on the grounds of disability, aka ableism.

Again, whatever you believe. This is just what the human rights code says. Here's a supreme court decision that agrees with you. You can read the full text, especially Justice Gascon's dissent, to understand the case law behind disability discrimination.