If I have articulable reasons for forcing entry due to some type of exigent circumstance, I don't hesitate.
Just so happens to one last night that started as a 911 hang up call. On call back the dispatcher could hear an argument and then the phone was hung up again. Called back again and heard the argument picking up steam but was told by the male there was no problem and to stop calling. Before he hung up, dispatch heard the female in the background say "I'm not going to let you hit me again" and then heard a crashing sound. On arrival I could hear the woman crying and him shouting. The door was unlocked and I walked right in, had it been locked and I didn't get a response in a very short time, I would have put my foot to it.
Also last night, I had three calls to the same address in a 45 minute span. I know all the players well and the female party is nuts. Not dangerous nuts...just nuts. It was quiet when I got there, made contact on the first stop to see how she was doing. She was hammered, he wasn't. She was convinced "they" were out to get her, but didn't know who "they" were. Didn't bother knocking the next two visits.
I've been on other ones where a violent argument was heard by dispatch and on arrival I hear nothing. I have no qualms about entering and can easily articulate in my report the need to enter to check the welfare of all occupants based on information I had available to me at the time.
Like has been said, there are way to many variables to give absolutes or even rules of thumb. It all comes down to "totality of circumstances" and whether or not you have a legitimate and articulable reason for entry. In plain english, that translates into common sense.
Never be afraid to make a difference