When you only want half a bagel and they are pre-sliced do you cut it in half or do you take a take a top or a bottom?

If you take a top or bottom, a full circle, you have to cut it to make a cream cheese sandwich and symmetry it not guaranteed.
If you cut it in half you can either take the hinge part or the two free pieces and top to bottom symmetry it assured.
On the downside, you have to cut it and return the unwanted piece bag into the bag. Someone else will have to eat the piece you touched and left behind. Feh!

What is proper bagel etiquette?

Definitely a first world problem!