My issue with fridging Coulson is that it takes a character and flattens them out into a symbol, a banner to be waved. And it just always feels cheap to me. Killing a fan favourite gets a reaction from the audience that isn't earned. And what's more, he didn't have to die. Loki stabbing him and Fury lying about it to give the team the push they needed would have done the exact same thing. Achieved the exact same story goals, and would have actually been a great meta-comment on the practice of killing a beloved character for a) shock value and b) to motivate other characters to action.
I get twitchy. Very, very twitchy. It may come from a lifetime of comics reading, and just anger and laziness at the trope. Particularly in Whedon's work, tho I have since learnt it was Marvel's call--not his. I was furious about it in Angel when it happened to Fred, who went from being a real live girl to an object to be fought over by two dudes, to a banner to be waved to galvanise Team Angel. But at least Amy Acker didn't lose her job over it as she got to play Illyria. I was beyond angry about it in Dr Horrible because it wasn't an ironic commentary on the practice. It was a straight-up fridging for no reason except he couldn't think of anything better. And Wash... Wash was the first time I really became angry, because it really was more about shock value than telling a story. And that bothered me so much as a fan AND as a writer.
And so I kept thinking the SMART thing was to play with audiences expectations that Joss would kill a character just because he has that rep, and that we'd get a reveal. Because killing Coulson only has an impact on the minority of hardcore fans who have seen all the movies multiple times and fanboy Clark Gregg. And that didn't feel like an adequate trade-off for erasing the character and the actor from that universe, to tell us something we already know: that Loki is a bad guy.
And the thing was... Loki could give a fuck. Coulson was just a dude who got in his way. Coulson's death was no different from the S.H.I.E.L.D. folks he killed at Project PEGASUS in Act I. They meant nothing to him. So, in terms of Loki as a character, the beat fell completely flat for me. Because had it been about killing Coulson because Thor cared about Coulson and was witnessing it? That I'd have bought. But not the way it actually played out on film.
I just tend to mourn lost opportunities.