The thing is that in the current setup of factions+griefing, it is possible to build a base that is literally impenetrable. This actually greatly annoys my friends and I, and if you could, GingerJonny, it would be much appreciated if you could reenable TNT. But, I know that that would never happen, so yeah.
And also, about the portals, that just makes the game TOO easy. Why make your own portals when you can warp to spawn to use the public ones?