Well these "useless invisible things" used to have a use. They could hold up an entire platoon in one base if crafty enough and could in a more useful role sneak into a contested base, blow up something important, and let the zerg capitalize on it. The infil in ps1 was a saboteur in the most exact sense. It sabotaged the bases power, ability to defend itself, its ability to spawn people, It turned of the lights and made the whole place dark as well. If a good or even average infil got into your base it would take a while to find him and even longer to repair the damage he did. But as you say its the playerbase that hated the infil. Even my comrades gave me a little hate and swore the infiltrator while I was on TS calling us spineless tricksters. Once an infiltrator broke the charades and revealed himself everyone and their mother flicked on darklight and went a huntin' for if they let him persist terrible things will happen. It's sad they removed the most unique class of the game and its neutered offspring has to resort to actually killing people to be usefull. How dreadful.
Apparently you haven't certed mines yet. Understandable; they're expensive. Once you get one, and a second one especially, you'll have some fun with them. Popular stairwells, jump-pad landing pads, gen hut doorways after you overload the gen, etc. I haven't ground up the certs for mines yet either. But in beta, I *loved* them. They really extend your power and ability to control certain areas. Having said that, the servers are so much more full at release that infing is harder in general. In beta, I could cap an outpost and might only have 1 or 2 opponents to deal with. Or perhaps 4 friendly versus 4 opponents. After release, it is big fights everywhere. If your mine takes out the engineer coming to repair a gen, there is probably another one right on his heels.
