Short answer: no, you are not being unreasonable to worry about it.
Long answer: it depends. As many people have pointed out, life is certainly better here than many other places in the world. But presumably you're not deciding between the UK and somewhere worse, you might have the choice of different high income countries. We also have the same privilege (husband is British, I am not, we have the ability to live and work multiple places and are therefore weighing up our own options). Most commenters here have probably never lived outside the UK and never will. There's absolutely nothing wrong with that, but their comments that it's fine aren't really helpful to you in your situation.
As others have said, if you have the resources to live in a good area with good schools and nice families, you can have a pleasant existence. If you have private health care, you can insulate yourself from some of the issues with the NHS.
But what I keep thinking about is my children's future, and what this country will look like in 10, 20, 30 years.
I look at how the education system is a mess, how we have lots of graduates with degrees that are not serving them well in the job market, while at the same time there are labour shortages in other critical areas (medicine, engineering) which mean we need to keep bringing in lots of immigrants. Obviously I'm not bothered by immigration, but high levels of immigration have had a materially deleterious effect on this country's politics!
Outside of unis, we seem to be doing a terrible job of getting young people into trades and other non-academic life paths, leaving many of them adrift and resigned to a life of low-quality, low-security, low-wage work.
Underfunding of everything pervades and undercuts all the public services in ways that intersect and multiply. Underfunded councils don't have the resources to put children with SEN into the settings they need, so they end up in underfunded mainstream schools which don't have the resources or staff to support them to learn properly. These kids often end up disrupting the classes (not their fault, mind you!) which then negatively impacts others around them. This happens day in, day out in so many schools across the country, year after year. So we're ending up with one group of kids not receiving the education they deserve because their needs are unmet, and another group also not getting the education they deserve because the limited teacher time and resources are disproportionately spent managing the behavior of a small group.
So I wonder: when these kids are in their 20s, 30s, 40s, what will the workforce look like? Who is going to be doing the high skill jobs of the future? Or will many Brits be consigned to a grim life while immigrants will come in, do the high wage jobs and pay the taxes that native Brits will live off via benefits (which already kind of happens already). Again, I'm very pro-immigration, but it feels so depressing if it's occurring because we're just not educating British children properly to begin with.
Sure, we can privately educate, and live in our middle class enclave, and try to insulate ourselves, but I'd rather live in a society where the median person is successful, rather than a place with high and rising inequality where I waste my children's childhoods worrying whether I've done enough to ensure their future success.
Anyway, as you can see I've thought about this rather a lot 🤣
Best of luck to you!