Why use Latin names?

A common question asked with respect to identification of various organisms in various groups, and which usually receives the same stock answers. These answers include, but are not limited to, some form of the following:

Why use Latin, rather than common names?
1. They are unique and international whereas one species can have several different vernacular names
2. They convey information about the species
3. Related species are listed together


However, consider how much of this isn't true.

1. They are unique
    > They are hardly unique! In theory, yes. In practice, keeping up with synonyms is an ongoing task. Studies show that scientific names change much faster than "vernacular" names, and if you use resources of various vintages you may need to know several names for an organism.
    > When I say "organism" of course these names may ultimately refer to several species which are later split (e.g. Hypnum cupressiforme), or there may be more than one name for one species which has previously been incorrectly split.
    > Consider that whether it's fungi (Philips) or botany (Stace) you will need the absolute latest to know what the current taxonomy is - assuming it has caught up, and you will probably need an older reference as you speak with people who use former names. By the time a reference is published it is in the process of going out of date and you will in fact need at least periodical literature to keep abreast of changes.

1. They are international
     > This is true at least in written form IF different authorities in different countries agree on standardisation. In practice, for some taxa authorities disagree, so one authority may or may not recognise the divisions of another. In pronunciation, no two people say Latin names the same, so you may have to write it down too.

1. One species can have several different vernacular names
    > Or none. Or one. I saw an Eastern Olivaceous Warblera couple of years ago. A week later it was in a different genus. Fortunately I only have to remember that I saw an Eastern Olivaceous Warbler, regardless of what taxnomists do to it. that's not the whole picture, of course, but it's certainly helpful - and at least a split between Eastern and Western Olivaceous Warbler is natural and memorable.

2. They convey information about the species
    > To a degree. On the other hand they may present false information given the frequency of reclassification that has to occur when things are later examined more closely.
   > They also mask information. The British birds we know as "tits" usefully are grouped together in English - they're similar in appearance and this grouping is helpful in the field. They are, however, now all in separate genera, which masks their similarity. (Note, I don't argue the division is unjustified - just that English names in addition are beneficial)

3. Related species are listed together.
    > ... until they aren't. You can only say this with any certainty when you know the species are related absolutely. Which we don't, although our idea of it is improving daily. Compare species order in a Collins bird guide of 2014 with a guide from 10 years previous if you doubt it! Up until the last few years you could say, as a point of fact, "related species are NOT listed together".

Basically then these points are all perfect in theory, in the lab and in maybe even in the future. However they are all at best half truths in fact, in the field and in the present. What could be useful, actually, is a standard English name around which taxonomists can pirouette to their heart's content.

Still, we've only been using this system for a few hundred years, so I'm sure it will come good in the end...