Sexual selection and the feasibility of altruism

I just came up with a fucking brilliant idea and I have no clue whatsoever why it hasn't been proposed before.

First, disambiguation. For those of you not familiar with Biology, prepare to be educated. The rest of you can skip ahead if you wish.

There are two primary forces in the game of evolution. You're all familiar, I'm sure, with natural selection. For consistency's sake, I'll quickly define it. In any given environment, an individual with traits (behavior included) more suited to life in that environment is more likely to survive and reproduce. A more accurate way of saying this is that for any given environment, the genes that give rise to traits most suited to their proliferation in that environment will be more likely to proliferate and, given enough time, dominate the population.
The other, often opposing primary force is sexual selection. This relies on the concept that individuals with more attractive/noticable/beneficial-to-partner traits will be selected for by the opposite sex and therefore more likely to breed. Again in genetic terms: genes producing more attractive/noticable/beneficial traits will be more likely to find their way into the next generation, and therefore, given time, will come to dominate the population.

These two often collide in interests, the simplest example of which can be seen in the case where the animal with the dullest coat will be less likely to be noticed by predators, while the animal with the flashiest will be more likely to be noticed by females. In this case, stabilizing selection takes place, where selection pressures are exerted on the population at both extremes, creating a trend towards moderation.

A controversy has raged in biology for decades over the issue of altruism. It makes no sense, from a genetic point of view, why true altruism would ever evolve (and nobody's saying that it has -- as far as I can see most acts of 'altruism' are committed with veiled or unconcsious expectation). By definition, an altruistic act is one that benefits another, with no benefit whatsoever (indeed, normally costs) to the self. It's clear how natural selection would overwhelmingly select against this kind of behavior, and so the existence of what appears to be altruism in nature today has perplexed all engaged in the study of behavior.

I ask: why have none of them considered sexual selection?
I'd imagine an altruistic mate would VASTLY benefit any individual, and so I would expect the tendency to prefer and discriminate for altruistic mates would spread through the population at alarming rates. As an effect of this, via sexual selection, altruistic individuals will be more likely to breed, and so altruist genes will become predominant.
However, not too predominant. We can't forego the everpresent hand of natural selection, which assures that any individual whose priorities are out of line will face the swift justice of genetic death. Between the two of them, a stabilization arises and both extremes -- excessive selfishness, and excessive altruism -- should be minimalized in favor of a certain trade-off. In fact, the most favorable tendency in this case would be the intelligent and careful discrimination between when to act altruistically and when to look out for number one. Could this be one of the primary factors fueling the rise of intelligence?
Intelligence-rearing or not, it stands that this is a remarkably sensible and simple way in which certain altruisms may have come to be just as easily as certain self-serving tendencies. In fact, it is in this way that altruism comes to be while still acting in a self-serving way -- not quite true altruism after all, but as close as is practical. Similarly, it offers insight into how selfishness and altruism could have evolved in tandem, going as far as to display how altruism and selfishness are truly two sides of the same coin. No doubt, your altruism is my selfishness, and vice-versa. In this way, altruism becomes a form of networked selfishness, in a "you scratch my back, I'll scratch yours" kind of way. It's easy to see how, keeping strength in numbers in mind, this kind of behavior could have held an immense advantage. Is this the source of society?

Possibly.
The concept as a whole is full of loose ends, and I've got some serious pondering to do before declaring a new theory of behavior (har), but I think it's an interesting possibility. Also, my argument reeks of genetic determinism, which may or may not be the correct way of looking at things. We'll see...