This is where logic comes in. Shut down all the relays. It potentially gives the Galaxy hundreds of years if not a millenia to stop the Reapers from crossing the intergalactic void quickely...
They can't shut down the relays. Only the Reapers are able to control the entire relay network. Even if the Council races could
shut down the relays, they never would because it would effectively destroy galactic civilization and commerce.
Plus of course, shutting down the entire relay network is exactly
what the Reapers want to do. Remember the Protheans were defeated over the course of centuries, with the Reapers in control they effectively shattered their empire by isolating all of their population centres then systematically going after them one planet at a time.
"Sending a fleet after them" makes about as much sense as launching a grape fruit at a freight train and would have be about as effective. As Hackett pointed out, it took multiple
fleets to take down one
Reaper and even then it was only momentarily vulnerable because Shepard destroyed it's avatar (quantum entanglement working both ways it seems.) If the Reapers move together in force (which is a fairly safe bet they do) then even if every warship in the galaxy swarmed them at once, they'd be a rapidly expanding dust cloud in about 5 seconds flat.
True but I'm talking about after the fact of discovering the true nature of the Collectors. Why go in after them...Why not just shut down or destroy the relay like they did here?
Aside from the points Skywalker
raised, there's also the possibility that the Omega-4 relay may not have been the Collector's *only* means of reaching the terminus systems or citadel space.
Leaving aside the pesky technical impossibilities of shutting down a relay (already known to be unstable) and the mass genocide that would result in wiping out Omega's star system, including all the other Mass Relays, thus probably cutting off a sizeable chunk of territory from the rest of the galaxy...those issues aside, taking out the relay doesn't solve the bigger problem: a lack of solid information. The Illusive Man correctly surmised that if the Collectors were indeed agents for the Reapers then not only did they need to stop them from taking colonists, they needed to know what they were doing with them, why and at the same time try to find anything they can that might give them an edge over the Reapers. The best way to do all that is to follow the Collectors back to their point of origin, find what out what they can (the Normandy was after all built for stealth recon), sabotage their operation and get the hell out in one piece if possible...or die trying.