This is ridiculous. We have been using HubSpot for a few weeks now and already the CRM is clogged with unknown Contacts and Companies and we spend more time removing then actually adding and working with the ones we are interested in.
It should be a feature to automatically add Contacts and Companies NOT the other way around. This should be basic core functionality that I as an admin can control who and when a contact or company is added to my CRM database.
As this basic functionality has not been fixed for a number of years, it might be because it benefits HubSpot and it is worth keeping it even if customers complain. 
We are already looking for other CRM systems that support smaller companies.