It's good that you think of these questions. However, there are some assumptions you made which made life "impossible":There's such a thing as the (shucks i forgot the name) habitable zone? It's a range of distances away from the sun where the temperatures allow water to be in the liquid state, hence allow life to form. a double-star system will wreck this zone by making it an "8" shape, or even a peanut shape if they're close enough. A planet cannot have such a strange-shaped orbit because it will eventually crash into either star, nor can it be far enough that it orbits in an elliptic because a far orbit would eventually swing it away by one of the star's gravity. It's a die or die situation. Even if there's actually a far orbit that can be stable, at least part of the time Earth will not exist in the "habitable zone", and that means ice age, and civilisation can't exist either. That's what i think. Abit confusing, because my thoughts are always like that ^^||
1. You assumed that the two suns will be equal in size, and hence contribute a significant effect on the orbit of the planet. In fact, if it were the case, the orbit of the planet will not be an '8' shape but rather a highly complicated orbit which is the basis of the N-body problem. Remember, the two suns will also orbit around each other. In this case, I would agree that the planet will highly unlikely to harbor any conditions stable enough to support life (highly unlikely, as there is always the minimal possibility that life can still exist beneath the surface and thus shielded from the effects of the radiation fluctuations). Based on current binary star data, most of the binary have one sun that is half the mass of the other. In fact, if you only count data from visual observations, it may be even less, with one sun 1/5 the mass of the other (see Figure below). I am not sure that planetary bodies in double-stars will tend to be elliptical if they are sufficiently far away from the binary system. I will run a few simulations to confirm.
2. If the planet is at the same distance from the two suns as Earth is from the Sun, then I agree that the planet would be unlikely to harbor life. However, if you move the orbit of the planet further out such that the total amount of radiation received is the same as what Earth is currently exposed to, then the environment may remain hospitable for life.
3. The conditions of a planet is not determined only from the distance from the sun(s), but also on the composition of the planet and its atmosphere. The atmosphere can buffer or aggrevate the amount of radiation from the sun(s). For example, Mars is 52% (78 million Km) further out from the Sun than Earth, and the temperature variation is from -8 to -113 deg C. For Venus, at 27% (41 million Km) nearer to the Sun, the temperature is about 482 deg C. The difference of the surface temperature between Earth and Venus is out of proportion to the radiation exposure from the Sun, and the reason, which you know, is due to the "greenhouse" effect of high CO2 levels in Venus. The interesting question would be: if we move Venus out to Mars orbit, will it have 'Earth-like' living conditions?
4. The 'habitable zone' is only applicable to life forms that depend on water. For life forms that depend on other (highly speculative) mediums life methane, the habitable zone is different.
Nonetheless, I agree with you that life would probably have a difficult time on such a planet. In fact, my personal view is that intelligent life is highly improbable in the Universe except Earth! Which is a pity, as I'm looking forward to joining the Starfleet Academy in my lifetime!
Cheers!
"The universe is composed mainly of hydrogen and ignorance." 
In fact, while wasting my life away in camp, i actually thought of an exception to my own rule! It is when stars are sufficiently far apart to make the habitable zones not merge, then each star can have habitable planets of its own!