Yes you play artifacts anyway, but you still need to pay mana to get 3 of them out (unless you went with some wacky W/G Tempered Steel variant that uses Memnite's and a bunch of free artifacts - I don't reccommend it by the way).
Monocoloured Infect works in Black or Green, but Red and Blue are just too weak on their own. What blue creatures do you play in a mono-blue Infect deck?
4 Blighted Agent
Viral Drake is too mana intensive, and Chained Throatseeker is expensive and can become a dead card easily. What does Blue have that black doesn't? Blighted Agent is only slightly better than Plague Stinger. Black can play Plague Stinger, Phyrexian Crusader, Hand of the Praetors, Skithiryx, Go For the Throat and discard spells like Inquisition of Kozilek and Despise. Blue has Blighted Agent and that semi-powerful counterspell. Mana Leak if you want to run that.
I think Blue/Black would be fun. Run the same sort of style as Black/Red Vampires.
4 Drowned Catacomb
4 Darkslick Shores
4 Inkmoth Nexus
12 Swamp
4 Blighted Agent
3 Necropede/Ichorclaw Myr
4 Phyrexian Crusader
3 Whispering Specter
2 Hand of the Praetors
2 Skithiryx
3 Mutagenic Growth
4 Despise
3 Infect counterspell (I forget the name)/Mana Leak
3 Go For the Throat/Doom Blade
3 Tezzeret's Gambit
2 Lashwrithe
Or something along those lines.