1/3 nl, 9 handed.

I guess this is more of a general question than a specific hand but let me try and remover the specifics as best I can.

Hero is bb with 100 bb

Typical loose/passive game, if someone 3 bets you're probably looking at kk+ preflop, and on the flop people are way too passive or timid too.

3 calls, hero looks st a6o in the bb and checks

Flop 668 with 2 spades. Hero checks (?), checks around
Is this a spot where you're okay playing for stacks 100bb deep? How deep would you have to be to consider ever getting away if action went nuts? Would you look to c/r? People may stab here with an 8 or a draw or they could even have an overpair

I just feel like if there's heavy action here you're likely beat, maybe I'm being scared but it's an unraised pot and your hand is sort of obvious once money starts piling in. Meh.

on this flop, getting in for stacks is good.
you lose to 88 who didnt raise? but 86 beats you.

Like you said, people play flush draws and straight draws.

So Bet flop, Bet Turn bet river and hope the A come and the flush

The old adage of 'never go broke in a limped pot' is just bulls*** imo. If we have a significant equity advantage we should be trying to get as much money in as possible, and some of the time our equity doesn't hold up and we lose a big pot. Coolers happen. As long as there are enough worse hands/worse equity that will continue vs our hand, we are printing money and should be ok that we will get felted some % of the time.

In the example hand you gave, there will be plenty of worse 6x and draws that will be willing to play for stacks, even if you play your hand face up.
And if people are really that passive or timid on the flop, than this should almost always be leading out here.

Yeah it feels like I've had more than my share of big losses in unraised pots, unfortunately. Could be runbad or just me not reading hands well but seems like I flop two pair or trips or some kind of pair+straight or fd and then end up losing a bunch. I need to get better at pot control, and if it comes at the expense of a missed value bet here or there then so be it, until my hand reading improves.

I won the hand in the op, for the record. Not that it really matters

This seems to be a missed opportunity, especially given the nature of the game you described. Thinking about our opponents ranges, it seems you're crushing almost everything and should be happy getting it in here.

FYI I ran this hand through Poker Cruncher to see what kind of equity we'd have in this hand. Thinking about what reasonable holdings our opponents can have (that they wouldn't raise preflop), I assigned the following ranges:

22s-99s
A2s-A9s and A2o-A9o
KTs-K2s and KTo-K8o
QJs-Q7s and QJo-Q8o
All suited and unsuited connectors
All suited and unsuited one-gappers

This is a pretty wide range that amounts to 44.3% of hands. Against 3 other players playing this range, we have 70.5% equity here on the flop. If we're heads-up, our equity jumps to 87.9%. I'm really comfortable betting this hand very strongly.

I would just donk out here. We're looking to start building a pot against flush draws / straight draws / 6x / 8x / pocket pairs, and yet at this passive timid table a lot of those hands will probably check back the flop (a disaster).

If heavy money starts going in for $300 stacks eventually (which likely wouldn't happen to the river given this huge SPR of 25) then we'll have to re-evaluate (mostly evaluating who is willing to get the chips in against us and what that person thinks of us); it's possible against certain players that we might eventually have to make a hero fold UI, but we'll cross that bridge when we come to it.

GcluelessNLnoobG

In general I get what you're getting at here, especially in this spot, but there are exceptions. I can think of lots of opponents off the top of my head that if they are eventually willing to play for $300 stacks in a starting $12 pot that I could easily make a river hero fold to without a fullhouse (as they are nitty enough to put me a fullhouse when they have 6x, so what does that tell me when they don't care?); these ain't coolers. Course, there are also lots of opponents I would never fold to here (as they would consider any 6x the nuts and would be happy getting in $300 stacks with it); if those guys show up with a better hand, yeah, more of a cooler.

Gitisopponentandactiondependent,imoG

I mean, yeah, we have an obvious equity advantage against the range of hands that we're seeing a flop with, no doubt. Furthermore, we also have an equity advantage against the range of hands that are willing to call bets (and perhaps even raise), no doubt.

But one thing that should not be lost in the math is what our equity is against hands that are willing to, for example, get in $300 stacks into a $12 pot on the flop. Against certain opponents, our equity in that case will be slim (drawing to our A outs) to virtually none (drawing to running AA).

Gitdepends,imoG

I lead out 3/4s pot on the flop here. You'll find out quick what you have going for and against you here.