To tell landlord of next door neighbours?

[Ezlo]

My next door neighbours regularly argue. They don't care what time it is and have two young kids.

Each time they argue they both say horrible things to each other and then I hear really loud banging. Possibly him trashing the place. I've called the police on them in the past. They also have a drug dealer visiting (via the back door) daily, I think demanding money.

I've had enough and so I want to tell their landlord to sort them the fuck out. WIBU to do so?

The tenants left after about 6 weeks. She did start court proceedings but they left.

Right, so no eviction actually took place.
Good outcome for everyone but there is no reason to believe that the same thing would happen here and OP could end up living next to someone very uninvested in the condition of their house and/or keeping their LL happy.
This is assuming the LL cares enough to do anything in the first place.

You can put what you like in a tenancy agreement but only a court can enforce it. The bar for anti social behaviour is very high - rightly so. It would involve official bodies like police etc, multple statements by independent witnesses, film and/or video.

If Mrs A and Mrs B (both homeowners) have a robust argument then they have to find some other way to solve things. However if Mrs B rents then it is clearly wrong for Mrs A to be able to weaponise the fact that Mrs B is a tenant to try to get her evicted. A court is not interested in interpersonal arguments between two individuals without some other cause - unreasonable noise, threats of violence, racist abuse, drug dealing etc.

Landlords who insert themselves into interpersonal arguments are risking a charge or harassment from their tenants. Its the tenant paying the LLs mortgage, not the snitch next door.