Put bluntly, if any aliens have FTL tech they could strap it on an asteroid and vaporize the earth. More simple than that would be to send nano-bots, an asteroid of significant size coming for us at any speed, or a thousand other things. Any civilization with that level of science/engineering know-how would most likely be like the US army going waging war with Neanderthals throwing spears.

So in other words the prospect of an FTL weapon is irrelevant?

Well, to us I think it would be irrelevant as it wouldn't take anything 1/2 as complicated or energy intensive to do in our planet. However, an FTL weapon could be relevant to an FTL capable species at war with another FTL species. What is interesting is that motion through space + motion through time must add up to the speed of light. So an FTL weapon would arrive at the target before it was launched if I understand the consequences right.

Sure there are.

https://en.wikipedia.org/wiki/Alcubierre_drive#Damaging_effe...

"When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong." -- Arthur C. Clarke

Thanks for the implicit compliment, but I'm not a distinguished but elderly scientist. :-)