My opinion is thatcwhen you're capable of purchasing your own home then you can have as many pets as you please. But while you are renting then you are bound by the conditions of your lease. Even if you rent a pet friendly place, you need to consider the possibility that one day you'll have yo move on. Its part of being a grown up entering into a legally binding contract. Considering the future is also part of being a responsible pet owner.
Is it the worst crime in the world? No. But it does mean you have no right to complain if your landlord breaks any conditions themselves.