We, at least I, were talking about conception, avoidance of it - once it has taken place the "project" is under way and then whatever the man wanted/wants becomes largely academic. Also, there are two "states": Committed long-term pairing (including marriage) and casual pairing (including going together many months, even years on the understanding that commitment is yet to be stated). Assuming a sole/contrary right to decide is far more damaging in the latter and in such cases it is presumptuous of the woman to expect the man to "be there" - she carried out a hijack and has no automatic right to expect him to wholeheartedly support her project. While, say in marriage, the circumstances are different, no woman should take any risk regarding falling pregnant if/when she knows he is reluctant to father a child. Before contemplating getting pregnant she should establish his aims in this. If the relationship means anything to her then she should either tell him he should have a vasectomy, have her own procedure done or else fastidiously take the Pill. The Pill is free on the NHS, no excuse.
To say he must guard himself against her is an admission that she is a risk to him. That said, the matter must be discussed and responsibilities fixed, there should be open honesty and no question of possible unilateral drift into romantic dreams of an offspring. Until men can switch off their fertility they are at a disadvantage with poor options by comparison. Yes, they are at risk but only if things are unclear/fudged and/or one or both proceeds/proceed unwisely.