The fact is that vast majority of sex offenders will always be a danger which is why you are probably safe to say you will not rent to known sex offenders.

Or any of them could be a sex offender.  

I've seen people let dogs loose on their neighbors, child predators that are already sex offenders running around the complex in their ankle bracelets, I'm a pro at kicking out armed drug dealers; hell, many years ago I LIVED in a building where the resident manager, who rented the second floor to the Devil's Disciples, thought it would be a great idea to let his pack of barely trained German Shepards roam the halls for 'security.'

If they have prior felony or misdemenor convictions in a list of areas (sex offenses, drug-related charges, dishonesty / fraud, violence, child or elder abuse) they are not qualified.  

Ontario Human Rights Code:People cannot be refused an apartment, harassed by a housing provider or other tenants, or otherwise treated unfairly because of one or more of the following Ontario Human Rights Code grounds: race, colour or ethnic backgroundreligious beliefs or practicesancestry, including individuals of Aboriginal descentplace of origincitizenship, including refugee statussex (including pregnancy and gender identity)family statusmarital status, including those with a same-sex partnerdisabilitysexual orientationage, including individuals who are 16 or 17 years old and no longerliving with their parentsreceipt of public assistance.

Getting your first rental property may or may not be as exciting as sex for first time..

I got sucked into feeling obligated to help them get what they wanted, when my obligation was to the boss.The next time I made a friend in the building, she started wanting me to make other tenants be quieter - as in having loud sex, or singing too loudly. 

It's especially handy when a tenant is angry and just wants to vent about something, like hearing their neighbors having loud sex LOLOL!  

Here is the Seattle definition: “Discrimination” means any conduct, whether by single act or as part of a practice, the effect of which is to adversely affect or differentiate between or among individuals or groups of individuals, because of race, color, creed, religion, ancestry, national origin, age, sex, marital status, parental status, sexual orientation, gender identity, political ideology, honorably discharged veteran or military status, alternative source of income, participation in a Section 8 or other subsidy program, the presence of any disability, or the use of a service animal by a disabled person.

It went from things like wanting me to let them have a washing machine in the unit even though the owner said no to them and after I explained it's because the pipes can't handle it and sorry, I'm not losing my job over it for you (in a very nice way) -- furious reaction, no more friendship.... to wanting me to tell their neighbor to stop having such loud sex (not kidding) and when I said I don't tell other tenants how to have sex (again in a very nice way, while giggling no doubt), I lost that friendship.