I hate the word ludicrous. I never hear philosophers use the word (well, at least not the good philosophers). This is a word used by sophists, yes, I did use that word. Sophists are the opposite of philosophers. From reading Plato, we learn that the sophists could be hired to teach young, aspiring politicians how to use rhetoric to befuddle challengers; sophists gave these power hungry and venal young men "talking points." Sophists did not teach their pupils how to construct an argument, weigh evidence, point out contradictions, or search for truth. Socrates did that, and the Athenians got rid of him for it.
The word ludicrous is almost onomatopoetic. Speaking or writing the word mimics its meaning. Flustered ideologues--from any political stripe--smirk, wave their hand, and sniff: "that is just ludicrous."
With this speech act they shut down any further discussion. We see this word popping up alot when pundits or "strategists" get peppered with a series of tough questions that might push them to find flaws or inconsistencies in their "talking points."
The Oxford English Dictionary(OED) teaches us that ludicrous has a long history in the English language. The archaic meanings--senses 1 and 2 (see below)--retain the Greek roots of the word: sportive, jest, playfulness (less emphasis seems to be on 'derisive' aka contempt):
If this is what we meant by ludicrous now, I would like the word. In fact, it would be a rather charming word. Instead, it has metamorphosed into the following meaning:
3. Suited to occasion derisive laughter; ridiculous, laughably absurd. (The only current sense.)
I find it curious, btw, that Benjamin Jowett's sentence (the famous translator of Plato)--"Plato delights to exhibit them [Sophists] in a ludicrous point of view"--is evidence of the current meaning of the word: "derisive laughter" or "laughably absurd." While most careful thinkers will come to see the sophists as absurd, this does not necessarily mean that we laugh, with a self-important tone, at their folly. This means that we find their reasoning to be flawed. Moreover, I have always admired Socrates' patience with dim and obstinate interlocutors, such as Meno (whose Greek name literally translates to 'I remain').
The phrase: "that is ludicrous" is evidence of intellectual laziness, if it is not followed by carefully reasoned claims that show why a claim is ludicrous. This is usually the fashion in which it is uttered, hence, why I this word raises my hackles.
As Socrates says in the Gorgias "submit nobly to the argument." Or, as Rod Tidwell says is Jerry Maguire: "Show me the money."
P.S. Check out Mad Sophist for a rather amusing example of sophistry.