Right, you lose money on each additional bet that goes in. The size of the pot makes up for it making it a profitable call, but you'd still rather not put in any more money with crap equity.

You're in position on the turn in a $100 with 20% equity. Your opponent can bet $10. If he doesn't, you have 20$ of equity in the pot. If he does, you lose $10 from your stack, and the pot becomes $120 of which you have 20% equity, or 24$. 24-10= $14 of value vs. $20 of value when he checks. His betting costs you $6, even though you have a profitable call.

If you are ahead and your opponent has say 9 outs to beat you, any bet you put in your opponent must match it. So he is getting even money on this bet on what is a 4/1 chance. The pot is irrelevant, if he hits he wins it, if he misses you do. There is nothing you can do about that, but you can force him to match an extra bet at good odds for you.

The main reason you bet here isn't to charge draws its because you likely have the best hand and will get called by worse. Its strictly for value. In LHE your equity advantages are usually rather small since your opponent is often going to at least see the turn and or the river if he has anything at all. Therefore its really about pushing your equity advantages as often as possible to slowly add to your win rate over the long run.