Can you point out some of the traditional practices of meditation that have no roots in religious traditions? I can't think of any truly secular traditions of the top of my head (or at least any that weren't invented in the last 50 years).
As for Buddhism, which is at the root of what most people mean by "meditation" today, calling it a religion is a bit problematic because it doesn't involve worshiping gods and, in theory at least, is not supposed to be primarily faith based. Both of those things: god worship and faith seem so fundamental to the western concept of religion that applying that term uncritically to Buddhism seems ill-founded.
So it is neither atheistic nor theistic.
Yes, the roots of meditation are in religious practices (as, are, arguably, the roots of every human activity). That doesn't mean that contemporary meditation practices are necessarily religious. Many aren't.
So if you're talking about the term "meditation" in general (as we were), to limit it to a religious practice is a mistake. It's much broader than that, even if it derives ultimately from something that once had a religious aspect.
But it also means that we can’t claim that there is an evidence base for the positive effects of meditation, and more than we can for ‘medication’ or ‘food’.
Meditation can be beneficial. Meditation can cause severe problems.
Both are clearly true statements.
The question is - what kinds of meditation are beneficial to whom?
It’s worth noting that the Asian religious traditions had a history of being very selective about who was taught.