Have you ever seen anyone manually detonate a land mine in any movie, war games, etc ??? This is ridiculous. Also it should rip appart anyone stepping on it. Otherwise you get a sci.fi game where every pub player will complain because the land mine is useless. Engies are already nerfed with their hp and classless objectives. Remove the power of their abilities and they become completely useless.
Inferno, having only the fire fights in a game is boring and elitist. Boring because this makes seamless games where you have no choice at all and only one strategy relies only on your tracking skill. Even cpma has more mechanics than that. Boring also because then you choose only the chars that have the best guns and thus you have 16 field ops mass murdering and 0 objective play. Then elitist because an objective player wont play such a game for long knowing he will get pawned and not be able to use his or her skills that can make a team win without firing a single bullet.
The land mines right now are great, nice blast and good crowd control. Plus it gives a meaning to Proxi, otherwise she is totally useless for 80% of the objectives. The stickies are a good idea, but there is no need to make them manually detonated. Manually armed can be a good idea though like lazer mines in quake wars IMO.
Edit: if a comp player gets killed by a mine, this means that someone was able to trick him and win by using a different set of skills. This should be recognized too as skill.