You are saying that because you are biased. Those on the left think that birthers are wacky and that there is nothing to it. Just like those on the right think that "Trump's ties to Russia" are nonsensical.
And here is a secret..shh don't tell anyone...both sides are correct! It's all a game of smoke and mirrors to influence the voters.
The idea is to berate our opponent by any means possible. Those in the know understand that it is all a steaming pile of horse crap. But the general populace follows along. The general populace on the right are currently upset over the talk about Trump's ties to Russia and the rest of the fake news that has been spread. The average Joe's on the left are saying "Yeah we knew Trump was no good".
And all along it is a fight to influence those in the middle who are not sure what to believe.
This stuff works and it has been going on as long as our nation has existed.