While Cicero is an important ancient source on Epicureanism (both De Natura Deorum and De Finibus Bonorum et Malorum contain long treatises on Epicureanism), he is not a sympathetic reporter — in fact “For the Epicurean philosophy Cicero had only disdain throughout most of his life, though his best friend Atticus was an Epicurean. This disdain leads him to seriously misrepresent its teachings…” (Internet Encyclopedia of Philosophy).
Quotations
"Let us imagine a man..."
“Let us imagine a man living in the continuous enjoyment of numerous and vivid pleasures alike of body and of mind, undisturbed either by the presence or by the prospect of pain: what possible state of existence could we describe as being more excellent or more desirable?” — Torquatus, in Cicero’s De Finibus, Bonorum et Malorum.
"For my part..."
“For my part I find no meaning which I can attach to what is termed good, if I take away from it the pleasures obtained by taste, if I take away the pleasures which come from listening to music, if I take away too the charm derived by the eyes from the sight of figures in movement, or other pleasures by any of the senses in the whole man.” — Epicurus
Sources
Cicero's Tusculan Disputations
This collection by Cicero is not about Epicureanism but contains important references.
"De Finibus Bonorum et Malorum"
On the ends of good and evil is another major work by Roman author Cicero. Books 1 and 2 present another dialogue regarding Epicureanism.
"De Natura Deorum"
On the Nature of the Gods by Cicero is written as a dialogue between Cicero and representatives from Epicurean, Stoic and Academic Sceptic schools. Book 1 contains the discourse of Velleius — a Senator and Epicurean — which consists of three parts: a general attack on Platonist and Stoic cosmology; a historical review of the earlier philosophers; and an exposition of Epicurean theology.
Arguments Against
The "intrinsic harmlessness of wrongdoing"
The argument generally goes like this: in Epicureanism, there is nothing inherently bad about wrongdoing (rape and murder, to take extreme examples). Therefore (the accuser often adds), Epicureans are the worst.