Everyone has the right to privacy in their own home.
Whether you own your property or rent it, the point remains that outside of exceptional circumstances, you are right to expect that you can enjoy living where you live without any unwelcome interruptions.
In many places, this expectation is backed up by the law, but it is not the same everywhere—and no matter where they live, tenants are the most vulnerable to having their personal space disrupted, thanks to nosy or overbearing landlords.
Unfortunately, there is a subset of people who rent out properties who can’t accept that a lack of complaints and getting the rent paid on time usually means that there is nothing to worry about. It is understandable not to want a property you own to fall into a state of disrepair, but that does not make it OK to be forceful in monitoring a tenant who is not doing anything wrong.