We probably need another species to compete against to unite us.

Nah, the US would use it as an excuse to demand a world government under their control.

Another species is very useful for unity, not necessarily for us to band together against, but because a proper intelligent alien kind of invalidates every religion. All the conflicts from culture clashing suddenly become pointless.

Or at least racists will have something else to look down on.

Throughout history men have joined with their enemies to kill their neighbors. Cortez had an army of native Americans with him to take down the Aztecs.

That Venutian amoeba will have to take one for the team. OUR team.

Dump all the billions into AI controlled nuclear weapons

When the aliens show up and demand who's responsible for why our societies are such shitshows, all we have to do is point towards the fancy neighborhoods

Now Mr Ozymandius with this one cool trick you don't even need to find the aliens.