I think this is really situational, per several comments already made. On our last trip, my wife's waistbelt pouch was chewed into based on lingering food smell (but no food); I certainly agree with the comment about keeping zippers/flaps/other openings open.

Last winter some others and I went on a day hike the morning after an overnight backpack/snowshoe trip, leaving most of our stuff behind. The others all had tents and left their gear in their tents. I had slept under a tarp, and had already taken down the tarp by the time the decision was made to hike around a bit before moving on. So I put all of my things in a black plastic garbage bag and tied it shut. On return, the tents weren't touched, but my yard waste bag had been ripped open by a fox and all of my stuff strewn all over in the snow. For some reason, it seems like many/most animals see a tent as "an object" and don't bother it. I expect if the food scent was strong enough, however ...

In terms of worrying about human thieves ... I think this is quite situational again. If you're hiking scant miles from a busy trailhead on a sunny weekend, it's quite different than camping 50 miles from the nearest road, and of course there's a lot of greyscale in between those relative extremes.

On a dayhike away from a base camp, my inclination would be to leave a tent sealed with things like sleeping bag, etc inside, and certainly no food or other scented item inside. Hang food (high enough and far enough out ...) or use bear can or Ursack depending on location. If marmots or goats are known to be an issue, certainly hang gear up out of their reach.

W.r.t. the human element, the thing that sometimes makes me worry a little isn't that someone will carry my gear away on top of their own, but that they'll recognize that I have something significantly nicer and leave their, say, cheap sleeping bag behind and take my good one. It's never happened, though, and life always has some element of measured risk. What good is the nice sleeping bag if you don't get out and use it!?!