Yea, I don't think it reasonable to expect every Senator to contribute to every single debate on every bill and as such we would have a lot of abstentions, wouldn't we?
On some bills there just isn't that much contention, whereas on others, the valid points might have already been resolved and thus there is no room for more debate. In those cases, just read over the entire debate and make a decision regarding your own opinions of the underlying matter, whether all the concerns are dealt with and then vote accordingly.
