Terrorists vs Keystone Kops

This is actually a thing, and it’s called “swatting”. A tip such as you describe *will *result in the local SWAT coming to your door, weapons drawn. They don’t wait for warrants or confirmation, they just go, because what if it’s not a hoax?

The police don’t stop all drunk drivers, but that doesn’t mean they’re incompetent.

There is a limit as to what you can prevent in a free country. There’s no way around that, I’m sorry to inform you.

No need to.
I just think your notion that the Paris attack was a relative failure from a terrorist perspective is rather bewildering.
I found your suggestion that you could, theoretically, do a better job to be rather questionable.