Once upon a time, like today? ICMP is most definitely only allowed situationally through firewalls today.
That kind of cargo culted tradition is how you end up with weird packet loss and VPNs that flat-out refuse to work.
I could be convinced to block inbound pings. Anything past that and I'd want solid evidence that it wouldn't break anything, with the expectation that it would.
I'd say that ICMP is only situationally blocked by firewalls, not the other way around.
Because I can ping almost any public server on the internet and they will reply. I can ping your website just fine and it replies to me!