ZSE Controller described a failed alert involving a potential conflict alleging ERAM/EDST should be 'fixed' or discontinued.

Narrative

Air Carrier Y was northbound and Air Carrier X was climbing out from SEA southbound. Their routes were 8 or 10 miles apart; laterally. As Air Carrier X climbed out; the EDST/URET was not displaying any alert on the two aircraft. As Air Carrier X flew past Air Carrier Y at one point they were about 6 or 8 miles apart with 400 FT altitude difference. At the same altitude they were a bit further. This is clearly within the parameters of a 'yellow' alert on the EDST. I called the SME over and had them do a report on this situation. Control of Air Carrier Y data block by this point was with Sector 32; but I had control of Air Carrier X data block. The EDST showed no alert; but when I pulled Air Carrier X up in the GPD; it showed both aircraft and in yellow; indicating a close situation. Dump ERAM or fix it. There is no excuse for an alert situation to be missed by the system like that. The aircraft were very clearly quite close and there should have been a yellow alert indicator. Even after I had handed off Air Carrier Y to the next sector; I had data block control of Air Carrier X and should have the alert on the aircraft. With URET and now EDST; our traffic scan is dependent upon the EDST giving us accurate indications of traffic situations and alerts. I have seen several situations where it does not; either giving false alerts or; as in this case; not giving an alert when it should. The younger generations of controllers base their traffic plan much more on EDST than the 'old guys' who grew up with strips and older-fashioned 'mark I eyeball' traffic scanning. If the computer doesn't show them an alert; they figure it must be okay. The danger here is obvious. The URET/EDST is presented as though it will give these alerts and it doesn't; or at least the ERAM version of it doesn't. Back to strips!