Is it wrong for an atheist to refuse to attend a sibling's religious ceremony?

Here's my twist on this topic.
I am an Objectivist and therefore an atheist and, as it happens, a professional engineer.
I have over the past several years designed and built several churches and church schools.
I have never misrepresented myself as a theist to any client - it has never come up.
My purpose is to build the best and safest buildings I can for my clients and I don't need to be religious to do that. I don't impose my atheism on my clients and they haven't tried to proselytize me.
I have occasionally considered whether I might be furthering the cause of mysticism by working on these projects, but two considerations have occurred to me :
1. These projects are going to be built whether I am the engineer or not.
2. If I restrict myself to only work for clients who share all of my principles and values my family will starve.

Are these just convenient excuses?

My clients are not violating anyone's rights. They're not kidnapping people and brainwashing them. They are freely engaging in a legal behavior that I think is misguided.
Would Howard Roark have refused to design a church if he'd had the opportunity?
And if he did refuse, would he have done so on moral grounds or because the project held no interest for him?