Anyone dies in my campaign, any campaign, there are consequences. Family may come after the killers, or maybe it was done because the PC's work for the guarde and this was an outlaw. I just think that there shouldn't ever be anyone that it's somehow "okay" to kill.

To me every death having a consequence is just as unrealistic as deaths never having any consequences.  The number of unsolved murders in even a small city can be quite high and that assumes a body was found in order to classify it a murder.  Otherwise it is a missing persons case and even then that assumes it was reported.  To me it as depends on the circumstances surrounding the death.

Many people feel it is okay to kill.  What do you think soldiers sometimes have to do as part of their job? However, there is a general belief that it is not okay to commit murder.  In many cases the belief as to whether a death is viewed as "killing" or "murder" may depend on the laws of that person's culture. So a wizard may feel it is perfectly okay (perhaps even necessary) to kill the evil necromancer, while the mortal cop may not believe it is okay to murder him.

If 100 shift potions are possible then why aren't all the NPC wizards running around with them?  I'd certainly expect something that powerful to be mentioned in the White Council's stats. If an ascension was as easy as making any old potion then Kelmer's apprentices would never needed to bother with creating a Darkhallow.

Seems more reasonable that the Lore x2 limit is in effect for potions as well as items.  (BTW page 400 defines a potion as an Enchanted item, so it is not unreasonable to rule potions have the same limitations as enchanted items unless specifically stated otherwise.)

Yes, but if that is what the players want, that they want to perform such an ascension ritual and accept that one of their number is a viable player character despite his new power level, should you not compromise and allow it?

No, that's not compromising.  Compromising is about give and take, you are asking the GM to do all the giving.  A compromise would be allowing the player to perform the ascension ritual as part of a campaign arc.  Something that would required one or more major milestones to complete.