Is this intended or will it be fixed in the future?

I noticed someone managed to place 3 barricades on my pillars outside(so much for raid defense…), and the worst part is they didn’t even seem to decay.

you have to pillar up all the way so they can’t do this. They can only place barricades on the top of pillars. However I suspect this will be fixed as well soon. A few patches ago you could place spiked walls on pillars and place boxes on the spiked walls to create a ladder.

Yea, if I pillar around my house I make sure it’s at least one pillar above the roof. They won’t decay seperate from your structure since they are considered part of your building now.