pog it is one thing to be passionate about your field. It's great to have that drive and to feel so strongly about something that you dedicate your life to it over everything else.
But having drive and passion does not justify being able to talk to people however you want without consequence. Sometimes people on mn do need to grow a thicker skin, but the onus shouldn't always be on those who are posting for advice - it is all about give and take.
And being too agressive can be counter-productive. How many people are afraid to post in that topic for fear of the responses? As a result how many people might buy a puppy from an unsuitable source; might have a dog put to sleep when it could have been rehomed; might end up with an unhappy relationship with their dog when they could have got help?
It's all about balance really.
Nothing wrong with telling someone that picking up a puppy on the m4 at the Bristol junction when you've never seen the parents or the home it's come from is a seriously bad idea and should warrant some thought as to where that puppy might have come from, and what conditions others like it are living inn.
Nothing wrong with saying that someone should have thought through their decision to get a puppy and that a dog should be for life, and that rehoming it because you weren't prepared for the poohing/chewing/jumping shouldn't be considered a reasonable option and this should be thought through carefully.
Nothing wrong with suggesting that if a dog snaps it shouldn't necessarily mean that dog is going to turn into an agressive monster, and tht with some training it might be able to remain a lovely dog..
But it's all about balance. You can put those points across without needing to throw your "expertees" into the argument. You can put those points across without needing to swear or call names or hurl insults, and IMO once you start name-calling or swearing you lose all credibility anyway.
We have lots of people on mn who are experts in their field, and lots of them are capable of giving good advice without needing to resort to being rude to people. Ticktock is considered expert on bf/ff/child feeding but as someone said up thread she doesn't resort to namecalling or intimidation - and I speak as someone who has had heated disagreements with ticktock in the past.
Moondog is a salt and has given excellent advice on the sn boards (she reserves her swaring for other threads, 
)
And so it goes on. If you're an expert in what you do then it's best to keep being known for being an expert, and approachable as such, for what you do, because once you start earning a reputation for being intimidating and unapproachable it doesn't matter how much you know. If people don't feel they can talk to you then your expertees means nothing.