If this were my building, I’d ask the EC to send a notice to the people who allow the door to slam to comply with whatever bylaw that exists that says you may not use common property (the door) in such a way that it interferes with the peaceful enjoyment of other residents.
Or there’s section 117(c) of the Act:
An owner, mortgagee or covenant chargee in possession (whether in person or not), lessee or occupier of a lot must not use or enjoy the common property in such a manner or for such a purpose as to interfere unreasonably with the use or enjoyment of any other lot by the occupier of the lot (whether that person is an owner or not) or by any other person entitled to the use and enjoyment of the lot.
As for the protest slammer, he or she should be sent a letter telling them that the original miscreants have received a Notice To Comply and that they should cease and desist immediately so that there can be no doubt who is doing the door slamming. They should be warned that if they don’t stop the deliberate slamming, they too will get a NTC and face possible fines, since their front door is also common property.