Oh, the exact purpose of forcing married women out of the workforce varied depending on whom you asked. But the wikipedia article does explicitly give
> Marriage bars provided more opportunity for those whom proponents viewed as "actually" needing employment, such as single women.
as a claimed reason for marriage bars, which is actually quite similar to "firing for the purpose of hiring younger people", though it's being spun as for people's good, not to decrease salary expenses.
In a world where 1) traditional gender roles and family units are the norm, 2) jobs are known to be a finite commodity, and 3) employers are expected to provide adequate wages and benefits such that employees can support their entire family, then it stands to reason that is a fairly straightforward example of benevolent sexism.
I would hesitate to ascribe identical motivations to everyone involved in instituting marriage bars; I expect that there was a variety of reasons people did it. Some people probably did feel like they were doing good for society.
But the effects were somewhat pernicious, because as usual people didn't think about second-order effects. Or in some cases first-order ones, like women delaying marriage so they would not lose their job.