To be fair I think Sleeping Tree Sap is actually legal. Atleast according to the uesp skyrim wiki thing. That and I have never actually heard someone in game say it was illegal.
So while maybe it would be frowned on, what Ysolda is doing seems to be perfectly legal. Besides alchemist seem to sell all sorts of nasty poisons and their recipes(well I think) Then of course you have the bar tenders. Sure ale and mead are perfectly legal(would love to see a prohibition like era in Skyrim...) could be just as dangerous if not more so.
So the way I see it Ysolda is no different then a bartender or an alchemist who sells deadly poisons.
Oh and Mjoll attacking over cabbage, that's just a dumb oversight in the reactions code or whatever. If it was done right, she'd actually just be trying to stop the fight. That and I don't think the NPCs actually recognize what was dropped. For all they know you just dropped the most awesome weapon in game instead of a pair of old dirty boots.
Also since when does Aela talk like a cavewoman?
But at least you are right about Muiri... Except for one small problem.
Yes she does ask you to kill an innocent person. However this quest is obtained through the Dark Brotherhood. Now last I checked Narfi was also innocent. A bit crazy sure. But from what I have heard of him he just keeps to himself in his families old farm.
You see where I am going with this?
In order to actually get the Muiri quest... you have to kill an innocent person. Potentially two others.
So. For her to ask you this you are no better then she is which means you really can't hold this against her.
Of course if you are a Good Guy and avoids the Dark Brotherhood then she wont ask you to kill anyone. In fact there is no reason to believe Muiri performs the Black Sacrament if you don't join. Why is that? Because Nilsine remains alive. It's true that things move more slowly in the Dark Brotherhood since there is no listener. But even so, Astrid gets the contract ready fairly quickly once you join.
Which leads me to this.
Muiri only actually wants Nilsine dead if you join the Dark Brotherhood. If you never join, then she never really wants her dead. Not enough to perform the Black Sacrament. Then again I suppose Muiri might not think it would work and only after several deaths, believed to be done by the DB does she decide it might work.
And in my personal opinion... yeah she is just batplops insane. lol