The Rev. Rosemary Bray McNatt reports that she was once asked by her son if she'd be offended if he chose a different religion when he grew up. She observes that as his mother, no, she and his father raised their kids to think and make choices for themselves. But as a UU minister, well... yeah, it would bother her.
I'm not sure my response would be any different. Just differences in nuance.
I grew up UU, so the choice was mine to stay or not (or, given the realities of my teen years abroad, to return to being an active UU or not...). Neither of my parents were ministers, so that element's not the same, but I'm not sure that it's different for any UU and their kids--save in degree. I know older members of our congregation who raised their kids in the fellowship--and some think of themselves as UU (but don't attend), and some attend somewhere, or here, now and then, and at least some have adult children who went off and chose very different religions.
For any parent, regardless of their faith, I think there's an ouch in that.
The roots of the word, religion, refer to those things that tie us (back) together, with each other and the holy. Having one's child reject those things for others tends to feel like one's less connected, disconnected from, not tied back together with... one's offspring. Ouch.
Would I be offended? Not by the act. Part of me would be pleased that my child felt the freedom to make that right choice (for them, for now)--at least as long as they felt able to be above board with me about it. But there'd still be an "ouch" to it.
Still, I can imagine reasons--people make these kind of choices in order (sometimes) to marry a beloved who is a devout and committed member of some faith tradition. With whatever reservations and mental Twister....
What would offend me would be having them reject the core values we've raise them with. Which are, of course, pretty UU. But I've talked with enough people who aren't UU, who listen to or read the seven principles and observe that they don't really have an disagreements... to know that there are plenty of people who share our values who aren't UU.
Like so many historic figures from the UU past, I guess I'm more interested in the universals of (our) religion than in the particular peculiarities of it, less devoted to the transient in religion and focused on the permanent.
Besides, one of my favorite Oliver Wendell Holmes quotes comes to mind; "We are all tattooed in our cradles with the beliefs of our tribes." If one of my children ever takes that step, I'll offer them my blessings on their journey, and observe (to myself, I hope, only) "You can check out any time you like, but you can never leave."