Most of the time I play a multiplayer shooter, which has objective-based modes (which don't just involve killing people), I notice how most people just don't care about the objectives and treat any objective-based mode as team deathmatch.
This is a big problem. Team work is nowhere to be seen mostly.
Therefore I think it would be a great idea to give no experience points whatsoever (or a very very small amount) for kills in objective-based modes.

Another thing is the obsession about kill/death ratios. Many people (including me sometimes) are so obsessed about their's that they won't do what is needed to accomplish an objective (like sacrificing yourself for the objective). Instead they camp or run pointlessly through the map in order to make some kills.

As far as I'm concerned kills and deaths in objective-based modes shouldn't be recorded at all as they do nothing for the accomplishment of an objective and are just a way to show of your elite skills.

Both actions I've listed should in theory stop people from abusing objective-based gamemodes as team deathmatch because they wouldn't be rewarded anymore and it'd become pointless to play like that.
It could make those modes unpopular though because people are used to killing enemies without end. Another reason why Armed Assault is rather unpopular because there you don't kill much as it is not really a shooter contrary to popular believe.

I'd like to hear your thoughts.

I agree that people throw the objectives out the window. I've seen a few vids on youtube during the demo where someone would be playing crash site but just be running around killing people. They wouldn't go after the pod once.