1. Anti-natalism prevents future risk, but we exist, so not only do we have to prevent new lives from emerging (if the premise that such lives would not generate positive value or permanently solve a problem is true), we also have to improve ours while they last. Therefore, we must be pragmatic and society-oriented if we wish to avoid the trappings of preoccupation with a singular cause; otherwise, we'll become witch-hunters, too attached to our particular "problem" to see the bigger picture. Plugging a leak is more important than cleaning its resultant puddles, but once you really have plugged it, cleaning the puddles becomes essential! Plus, abstaining from the act of producing offspring is not a total solution to the problem.
2. The premise that humans should not reproduce, like any other premise, is conditional; therefore, whether something of greater value ever presents itself in the future should be taken into account before we decide to make such confident, absolute assertions as, "No one should ever reproduce." Remember: From a fundamental standpoint, absolute generalizations are part of the core problem of our existence -- namely, brain logic shortcomings, which descend from the process of purposeless and inefficient evolution, which descends from the lack of an overseer of that process. Any "ism" that I can think of is part of this problem, as it is necessarily self-limiting, forever impractical and ineffective by design. Want to make the world a better place? Don't create or promote mechanisms of memetic exclusion.