At some point they go in and there is no way to know there is nobody else there of interest or who could kill them. This gets back to having to be mind readers again.
Really? Why not? Gotta get home and catch the next episode of your favorite cop show where your tactics are glorified?
#1 You never know who else was inside and connected to the crime without going in.
Are you actually saying that because there may be some risk, everyone should be subject to overwhwelming force? You talk as if every dealer is sitting on an arsenal. Thats in the movies. Have you forgotten that a person is presumed innocent, so maybe tearing his house apart based on an unverified tip might be a little unreasonable.
#2 You never know what other bad things they have inside and who has them still without going in.
So knock on the door, serve the warrant, and move in and secure the home. Not many people are really looking to shoot it out with police. If that scares you, join the fire department.