This excuse likely comes from a place of genuine care for the suffering of others. There are, however, a few issues that should be noted.
Firstly, it presents a false dichotomy; that either 1) humans continue to reproduce (or even reproduce more), or 2) wild animal suffering increases in its scope (and perhaps intensity too); but, these aren’t the only two possibilities. Even if, for the sake of argument, we accept – as it is not obvious that this is always the case – that areas occupied by human activities contain and generate less (nonhuman and human) suffering, it’s not clear that this activity must rely significantly on procreation. With Homo sapiens’ ever increasing technological capacity and store of knowledge, displacing wild animal suffering without using flesh and blood humans as a means to this end does not require much imagination to picture.
Note: There is an ongoing discussion within anti-natalist (and other) circles as to whether the human species will have to persist in significantly reduced numbers to ensure the ongoing mitigation of wild animal (or other forms of) suffering. This eventuality would rely on some level of reproduction but nowhere near the level present today and is not relevant as an argument for procreation until such a time is reached.
Secondly, even if we acknowledge procreation as a tool for reducing wild animal suffering, it’s an extremely crass and blunt one. Take the suffering generated to maintain a human life, add the unnecessary suffering intentionally imposed on others by that human and then consider the suffering experienced by that individual themselves; does this not seem like an awfully roundabout route to take to reduce suffering? Surely using non-sentient organisms, tools and objects to mitigate the suffering of sentient beings would make more sense? (Even if we cannot effectively achieve this at present, isn’t it worth focussing on developing those capacities, rather than thinking up excuses for procreation?) And finally on this point, the use of sentient beings as a means to an end in general should be viewed as highly suspect and should not generally be encouraged.
Lastly, as mentioned earlier, this excuse is not universally applicable. It does not apply, for example, in areas where there is no – or very little – wild animal suffering. Establishing a settlement in areas inhospitable to much of or any sentient life (such as deserts, the antarctic or outer space) would run counter to the objectives that the proponents of this excuse hope to achieve: reducing suffering, as the new settlement would establish suffering where there was none, or more suffering where there was little.