[DAO Spoilers] How do justify trusting Bhelen?

I'm replaying DAO for the fifth time and I always get stuck on Orzammar decision, but I always choose Harrowmont over Bhelen for one simple reason:

Bhelen is a really untrustworthy douche.

Your first mission to gain his trust is by sending out forged Harrowmont letters. But Bhelen doesn't tell a why or a who, he just wants someone to do his dirty work for him, and he's betting that The Warden is stupid enough or amoral enough to simply turn a blind eye to his obvious treachery against who wants to actually help him.

So how can your character trust him that he will help Ferelden and be progressive when the first thing you can do with him is lie to your face? Hell, everyone who speaks of Bhelen will say so: If he's still standing, every battle is a victory for him.

The only logically justifiable way to support Bhelen is if your warden is an Dwarf Commoner since he helps your sister to become a noble.

I know what's the outcome of Bhelen and Harrowmont rule, but I simply cannot justify why my character would place his bets to the betterment of Orzammar to a lying and treacherous ruler.