S1 relates to a topic on which many have strong normative feelings; S2 does not.

OK, so the issue is the social expectations about whether the issue is controversial and whether one is expected to have a normative attitude towards it? And in such a case, all statements will be interpreted as normative unless there are explicit disclaimers to the contrary?

I'd expect you to know that the assumption in my first paragraph exists

No, not really. I rarely speak normatively and in such cases I'm explicit about it. Typically I make descriptive observations, possibly with a variety of connotations and implications, but they are almost never of the "so you should believe/do X" kind. Normally they are of the "this is complicated, are you aware of this trade-off and that internal inconsistency?" kind.

I do set gotcha traps on occasion, but the sense of fair play usually makes me point them out beforehand. People still fall into them, anyway :-D