Even if you completely buy that line of thinking, your bomb is predictably likely to cause someone pain. So even if they believe it, they're acting inconsistent with their beliefs.
It is very much consistent, a person - intent to have children isn't a single node. It's a whole tree. If you cut the tree at the stem you likely reduce net pain experienced by orders of magnitude.
Most people don't think this way, but it is very much consistent with their views.
Buddhism acknowledges that life is suffering. Life is never perfectly free, easy, or comfortable except for a lucky/selfish few thousand, but there is making it better and making it worse. Cutting off USAID food for starving people is bad.
I think most religions teach something along the lines of "life is sacred" (definitions of "life" may vary). Without this limitation or common sense, priorities may get inverted and someone decides that people being alive is the "cause" of problem X (suffering, climate change, whatever). While it worked for Stalin and the Unabomber, it doesn't sound like a moral, healthy, or sustainable approach.
It's entirely illogical and unreasonable, but the urge to be noticed along with delusions that this will "change things" are overwhelming to people stuck in their own dark worlds. Plus, there are mental health concerns that go without saying.
