Is all competition good competition?
I think the discussion between Nr Mac and Dobbo Dobbo is a very interesting and important one; I am with Mr Mac in thinking that some potential new routes or airlines might have an overall negative impact.
A key factor is whether a new entrant is offering a lo-co style point to point product or an entree to a new hub with many onward connections. Thus anything which might limit the daily frequency on EK could disadvantage some of the huge number of people making onward connections whilst positively impacting only those flying to the single new destination.
In this respect CX would be good competition because they offer not just a way of getting to HKG, but many onward connections in Asia and Australasia.
Thinking of routes which could possibly experience "bad" competition, I guess Madrid and Lisbon spring to mind; if low cost competition forced out Iberia or TAP, many destinations in Africa, South and Central America would become much less accessible.
I think the current uncertainty surrounding links from BHX to the US may be a live example of this phenomenon.