It's not clear we need a Earth II with our current level of technology. We can now make water, oxygen, fuel, metal, robots, and so on. An earth II would obviously be more ideal, but there isn't any available.
Interstellar travel is certainly a very very high risk concept all by itself. We don't even have the ability to send unmanned things to another star, nor do we have the ability to have humans hibernate for any period of time on earth, nor do we have a clear path to either of those technologies.
Moreover we don't know where any earth like planet is. Even if we nailed interstellar travel, chances are we'd arrive at another star system and discover that we didn't have the things we need to colonize the planet (do we need to live in domes? Or floating cities like on Venus? Deal with hot temperatures? Volcanoes? Is solar power available in high quantities or not? Assuming we are looking for somewhere with an atmosphere, how strong winds do we need to design for? What chemicals do we need to be equipped to filter? And so on and so forth).
Nor is extinction the only goal we are talking about here. We also benefit immensely from communication with more people. We can communicate with mars, but not people on other stars. We benefit immensely just from the inspiring achievement, which we don't really get if we (and our children) won't live to see the success or failure of the mission. And so on.
Successful establishment of a colony on mars is of course not without its own challenges. I think the risks I mentioned at the end of my previous post will mostly be about what it takes to establish a colony once we can get their, not the getting their. But the chance of success is obviously far higher with current/near future technology, and the value of success is greater.