but we wont hurt you. We'll just slowly drive you insane until you become one of us.
Although really, a lot of things in life have potential bad outcomes. That doesn't mean you shouldn't do them. Life would be boring without risks, you just should be minimizing the chance of those risks having a bad outcome.
But those are not my only reason, as others have already indicated various possibilities.
Personally, Romances in games are a secondary concern. And as one can develop strong feelings of friendship towards certain NPC's in various Bioware titles without sex being an issue (eg; Varric, Aveline, Mordin, EDI, etc), the idea that sex being necessary is apparently invalid. Yes; sometimes friends can be enough.
And in the case of Romances, sexual intimacy is not required to have a fulfilling relationship. And I support the idea of making this optional if needed, though it already may be to a large degree.
What I dislike is Romance being tied to survival (eg; Miranda), being accidently accessed (eg; ME1), and other linked mechanics. These tend to be more annoying, IMO.
Also, have known at least one RL couple that had issues with the male Player becoming involved with every possible female in the game. It was soon after their discussions that he also was discovered to be doing much the same in their relationship. In this case, the female Player simply bolted. However, perhaps in game this situation should be reflected by having Ash, Liara, Miranda, Tali, etc having access to their abilities in which to better clarify their idea of loyalty.