There's too much room for error, if you let there be a line between what is and isn't patentable with respect to software. Better to leave it open and let the cards fall where they may. Software patents actively restrict technological development.
You both agree that there is major variation in how much "effort" goes into producing patentable work. Your problem is you want a very clear-cut definition specifying what is patentable, and since effort is hard to measure, you'd rather just throw out all patents. You assume this would be better than the current situation (which, I think, takes the other extreme - most things are patentable).
But why do you think the way you suggest is better? Just because the current system sucks?
Ultimately it would be better because it would eliminate patent trolling and foster software innovation. Right now a lot of innovation is hamstrung by software patents. I don't think any company should have the right to enforce what software someone makes, at all, ever.
Half of the tech industry with respect to software is finding something someone else is doing, and building on that but making it better.