What you're going to see now are raiders jumping walls or simply walking into towns and massacring everyone. It will be made easier by false sense of security that will now pervade the server. This is far more detrimental to town life than the behind the scenes raiding that was more commonly seen. The goal of behind the scenes raiding was to, at the smallest cost possible, access and seize the most valuable materials and then get out. Common building materials were rarely, if ever, touched as were tools of a tier lesser than diamond.
Now all that's left to do is armor up, invade the town, then slaughter as much as you can before ender chesting drops, if any, and committing suicide if no exit is available. Alternatively, a raider will enter the town and claim anything that can be accessed and ender chesting that before committing suicide and repeating. I would guess that most people are a little more careless with their building supplies (I know I am) due to the sheer amount of them collected and stocked and the inconvenience of making a secure location for them, and so it is building supplies that will be stolen. So while towns may now have more funds for their generator, they're not going to have much to build with. And then there's the fact that you won't have an opportunity to build to begin with because you're always under the threat of invasion and death.
Trust me when I say this: A cannon to gain entry is a rare thing. We cannon so we can walk out. No one is any safer if they do not build a maximum security wall around their town. So while I do like these changes for the most part, this is going to go very poorly if no alternatives are presented in the very immediate future.