Rhubarb, I'm guessing that you haven't been an extended bf-er and that this is why you're so sure and so insistent that it's not "necessary".
If you need to believe that for your own peace of mind, that's fine, but you need to be careful about what you say on a public website because it's not correct to say so categorically that bfing - extended or short-term - is no longer necessary in a developed country.
The truth is that no-one knows for sure, but current research suggest that bfing has profound, probably lifelong effects for some people.
This sort of stuff is upsetting for ff-ers to read and so l'll leave it at that, but there seems to be a strong dose-dependent effect of bf for a lot of risks. In other words, it's not just important whether you bf or not, but also how long you continue. So, how long should that be?
As far as I'm aware, there is no age where you can confidently say that bf stops being useful. But if you had to guess, it's quite likely that the physiological duration of bf - around 3 years for humans by many accounts - reflects the point where for most people the costs of bf (to the mother) would start to outweigh the health advantages (to the baby).
By then, of course, the advantages could be quite small and are probably related to maturing the immune system rather than nutrition - but as we can't for obvious reasons study this in developed countries, I don't think it's something we can make confident pronouncements about, either way.
(I don't have a personal axe to grind about extended bf by the way - mine both self weaned when I was pregnant, at 19 months and 25 months, so clearly I'm not up to gorilla standards here.)