Originally Posted by Vlerchan
I'm not asking for just reasons (which it seems you have given me). I realise that there's reasons that individuals disadvantage themselves.
I'm asking for a logical basis, i.e., one that does not appeal to emotion, for altruism: there's no logical basis, i.e., a basis that does not preclude emotion, to 'help others' (feel free to offer one), and disadvantaging oneself to achieve something else sounds likes it an actions being commited in ones self-interest. 
I don't study biology, and I don't pretend to know about evolution all to well, but isn't the base of it all to survive?: evolutionary speaking, I don't believe we'd develop pure altruistic traits, because disadvantaging oneself in favour of another would be counterproductive to our own survival.
I believe that if we develop altruistic traits, see: Homo Emiritus (I think?), then it will be because such traits aid in our own personal survival - and thus such traits won't actually be altruistic, as I defined it, at all
It's illogical to define a greater good, because an objective 'good' or 'bad' doesn't exist.
In such a case, ones actions would only be logical as long as everyone presumed that the outcome was also logical - or in the name of 'the greater good'
I'm presuming that altruism, the want to do self-defined good, plays a larger role than ego, the want to feel good, in ones decision-making process, because I've gathered that from personal experience. If it was a case of an action being commited entirely on the basis of ego, then I might be inclined to agree, but I don't believe this occurs all too often, if ever.
Since altruism, defined as: commiting a selfless action, an action not in ones self-interest or bringing one equal gain, is drawn from emotion, and thus illogical, I would label any action (or belief - left-liberalism, for example) influenced by altruism illogical.