Not two footed - Agree.
Not lunging - Tenuous, but agree.
However they aren't the only considerations in serious foul play, and I think people may have missed the real reasoning. Excessive force. I personally wouldn't disagree with the card on this point.
I'm also going to defend Chelsea on a related point (forgive me). It wasn't their reaction that got Ibra sent off. I've watched the video several times. Before the Mob get to him, he's unfastening the top pocket ready for the red. Oscar's reaction maybe, but not the Mob. Ibra's accpetance also tells it's own story. He knows he's overstepped the mark, hence no histrionics. There have been recent occasions in the LFP where he's been deservedly sent off too and reacted like an idiot - confronting all and sundry because he'd been "hard done by" as he stated in interviews..
I make this point for a wider learning reason. On more than one occasion I've seen a red card challenge (both SFP and DOGSO) and I've made up my mind. While I'm fiddling with the velcro on my back pocket (that's where I keep my red) and trying to isolate the offender, I've had the mob baying for blood. It's not influencing my decision at all - I've already decided. However the other team have started on the "You let them get to you" line. It's blatantly untrue.
If or when it happens to you, just think about that. It's too easy to blame players, particularly when their team has something of an unsavory reputation.
In the case of the PSG-Chelsea game, in that sense it's good refereeing. Made the decision early and stuck to it. If anything Terry and co. delayed the showing of the card by getting in the way.