I have yet to kill Connor, side with werewolves even recruit Loghain because......I am weak.
A tip for roleplaying the harsher, more pragmatic choices if you're too goody good to make them otherwise: try playing a dwarf. A very angry one, with no time or patience for beeswax. The dwarf noble worked better for me on this because you come out of that origin hating everything and everyone, but the casteless one works too if you play it from the right "too tired to give a sh*t anymore" angle.
Because dwarves have no contact with magic and are generally distrustful of it, it becomes easier to roleplay those harder choices as being part of your generally magic-fearing persona. Getting mages to perform a weird ritual? No way, let's just kill this demon kid before he destroys the entire village and castle and the army you came here to get. Later in the Dalish quest, take the same angle - creepy mage using creepy magic to curse innocent people and unnaturally prolong his life? Nothing an axe to the face won't fix. Pretend the cure dialogue isn't there, you're not even giving him the chance to explain himself. Then when you go back to camp and the elves attack you, you can roleplay that, ooooh crap you only meant to kill the creepy evil mage, this has gone way worse than you planned; now you have no way out but to kill the rest of the elves before they kill you.
At the Landsmeet, recruiting Loghain becomes a whole lot easier too - you're a dwarf, your entire life beats to the drum of fighting darkspawn. You know what and how many they really are, the threat they really pose, what a difference even one more Warden in the ranks can make. Alistair still has too romantic a view of what the Grey Wardens are, but you know the ugly truth is there is no end to the spawn, and you need warriors, not legends. If you have to lose one hopeless romantic to gain one more no-nonsense sword, so be it.
If you have trouble making these choices on more balanced characters, try channeling your most angry, helplessly impotent side and taking it all out on a Warden who just doesn't care. Anything to stop the Blight, as Duncan says. It's hard to stay in character at first and not mellow out down the road, but a playthrough that is the reverse of all your usual choices can be surprisingly cathartic in the end, exploring sides of your psyche that you don't even know you have.