I noticed on the BBC website that an MP is calling on people *not* to bag their dog poo but to use the stick and flick technique (which the Forestry Commission endorse in some areas.)
This is a response to people bagging and then leaving... sometimes (although not always) in non-biodegradable bags. Instead of encouraging them not to leave them...
I reckon that few people anti-social enough to deliberately leave a filled poo bag behind are going to hunt around for a stick and then, successfully, flick every bit of poo away from the footpath far enough that no-one is going to stand in it. (Bearing in mind that if you want to look closely at a plant you might step off the path, or you might be an orienteer)
I am however mystified by how few people take anything to put the used bags in so they are not having to walk along swinging a stinky bag (and tempting some to leave it, but not necessarily remembering, intending to collect on the return, . I didn't last long as a new dog owner before I researched this. Sadly the brilliant but perhaps not aesthetically lovely Muksak is no longer produced (due to retirement) but there's the Poop Pot and the Dicky Bag. If those seem pricey, then there's always tupperware type containers.
Aside from that, although dog poo breaks down, it has an impact on soil conditions thus damaging the local flora.