Part of the prorblem with "liaise" is that Microsoft has it wrong in their spell checker (ie it corrects to "liase/liason" ): I keep on meaning to contact them to tell them!
As regards whether it is just snobbery to be pedantic about grammar, my mum's argument is that what is important is clarity of communication. Many of the rules are there to aid comprehension and reduce ambiguity.
Therefore, the use of dialect/patois is fine in the local environment as long as you are aware that you are using it and can "translate" into standard English when appropriate.
By the same logic, the use of a split infinitive is OK, as often to avoid it clumsily will in itself alter the meaning or emphasis. It's interesting that I don't think any of the "grammarians" here has (or should that be "have"?) supported the rigid avoidance of split infinitives.
One of my (other) bugbears here in the West of Scotland is the incorrect use of the past particle: for example on TV last night a spokesman for East Renfrewshire Council said something like "We have went to an indepedent valuer". Aaaaagh! The worst thing is, they don't even KNOW that they've said anything wrong! Another common one is "I seen ....." That is when I become (more of) a snob: it just makes the culprits sound un-educated.
I too learnt the majority of my grammar via Latin and other foreign languages - but I also had a strong influence at home, plus, I suppose, a curiosity about how languages are put together. I even enjoyed learning about gerunds and gerundives!
Isn't it interesting to have Tech making comments - he's suddenly become a real person with his own opinions, instead of just the genius who keeps this site running so smoothly!