"All other things equal, having and raising children is a service to society."

[angus]

Yes.  Society is the natural condition of a social group, or a group of one's fellows.  Nurturing fellows contributes to the fellowship.  I don't think this is controversial because the syllogism is coherent.

Society can be cruel or polite, bad or good, but however fit or unfit it may be, it is propagated by its members, and those who add to its membership are propagating, and therefore serving, the society.

[angus]

it does not always hold true as a general statement

Well then, let us try another form of syllogism to convince you.  Here, we will attempt a proof by contrapositive.  The original proposition can be restated as "If you bring forth progeny, then you are serving society."  The contrapositive we will try to demonstrate is, therefore, "If you are not serving society, then you do not bring forth progeny."

Assumption:  You do not serve society.
Definition:  Society is aggregation of two or more individuals.
Restrictions:  Reproduction is achieved by sexual means only.

Not serving society means not communicating with other individuals of your species.  Without communication there can be no intercourse.  Without intercourse there can be no sexual reproduction.  Without sexual reproduction you will not bear children.

Quod erat demonstrandum

[angus]

Danke.

(Ich kann das Lesen, Schneemann.  Ich habe in Deutschland gelebt.)

[angus]

Other things are never equal.

Even if you take that as part of the conditional statement, then the proposition still holds.  In the logical implication (aka material conditional), the implication holds when the first operand is false, no matter the value of the second operant.  In other words, when P implies Q, and P is false, then Q can be true or false.  This is a well-established logical outcome.  (See, for example, "truth table")

[angus]

Having children is the evolutionary purpose of humanity.

Not just humanity.  For any living animal there really are only two important things:  food and sex.

We're above all that, of course, here on the forum in our little electronic ivory tower.  At least we let ourselves think that we're above all that.