" it's not of the same structure, you'd at least have to make it "a girl wants to have her fun" to argue that"
OK, there is an ambiguity as to whether "a" is universally quantified but it doesn't change the argument. The sentence you suggest has converse (equivalent to "someone who blames their tools is a poor workman") "someone who wants to have fun is a girl" - which surely you can see is not something you can logically deduce from the original sentence.
I'm surprised that we're arguing about something that is so fundamental and basic in logic, there is a simple right and a wrong here - if I said that 2 + 2 = 4 you wouldn't try to suggest a different answer 'cause you interpreted the 2 differently would you?
A poor workman blames his tools is the same as
If "poor workman" then "blame tools"
People use it to mean If "blame tools" then "poor workman" an obvious converse error. Thats' it, I cannot see any room for debate here.
"i wouldn't agree that the logical meaning of a sentence isn't comprehensively or exclusively dependent on its surface lexigraphical structure. i think you would have to have a strange, unrealistic sort of programmatic idea of language to think that, but i think it's implicit in what you're saying. (i'm not arguing that a sentence is the smallest meaningful logical unit in language incidentally.)"
Do you want that double-negative in there?
"i'm not arguing that the proverb means that everyone in the class of people who blame their tools is necessarily a bad workman, just that it happily does its job, which is to make an inferential claim leading from the blaming of tools to put it another way (rather than a deductive claim leading from the condition of bad workmanship) which i think that sentence structure does no problem"
Yeah, it does its job in that people understand what you're attempting to say, I'm just pointing out that it doesn't actually say that. It's the same as when someone says "I aint got none" and you understand them to mean that they haven't got any, it doesn't mean that it makes logical sense.