https://www.newsweek.com/spate-attacks-catholic-churches-fra...
https://www.thetimes.co.uk/article/vandalism-at-hundreds-of-...
That's the very definition of speculation.
"speculation seems quite unfounded"
Purely a matter of personal opinion. There is a clear trend at play in France that is very uncomfortable and disturbing. I think it's lunacy to ignore it. But to each their own.
That such speculation is often met with animosity is strange in itself.
The conspiracy theory, if there is one, is that there is evidence of arson, but it's being suppressed by the authorities. I'm explicitly not taking a stance on that.