You can eat tacos left out overnight.
As long as it's only been one night that the tacos have been left out then the taco is likely just fine.
I've personally have left a few tacos out overnight and then the next day I checked to see if they were bad and they smelt okay and tasted okay.
Nothing was wrong with the tacos.
I ate them and have not gotten sick from them.
However if the tacos were left out for a few nights then they should be thrown out.
Although it's not recommended to eat leftover tacos that have been left out overnight it's okay to do so.
Food establishments have to follow general guidelines for health regulations and although they say you should not leave tacos out overnight or longer than a few hours that does not mean they will actually be bad.
I try to remember to refrigerate any leftover tacos overnight but sometimes I forget and I won't throw a perfectly good taco out if it is actually good.
Just smell it, taste it or look at the taco and if it smells bad, has mold or a bad taste then throw it out.
Otherwise enjoy the taco.
I've been eating tacos left out overnight for several years now and have not gotten sick from it.
It's possible to get sick from the tacos but it's unlikely.