Let's assume a titan has T:xboxhuge, Sv:2+ and 100 wounds. For a gaurdsman equivalent, you need 7,200 shots to down it. For conscripts, you need 10,800 shots. Now, a full squad of conscripts costs 150 points and can put out 150 shots at most. That means you need 72 squads of conscripts, or 10,800 points (well, actually 21,060 points at minimum when you consider HQ and platoon requirements) to kill a model that's at most 2,750 to 3,000ish points.
Now, this creates another issue. For the amount of dudes needed to kill a titan, the opponent can take 4 titans, or 7.6 titans when you include having to fit dudes in FoCs. That means that while you have enough fire power to kill one titan in a turn, you still have 6.6 other titans to deal with. And if you take more dudes to deal with that, the opponent gets more titans. So you'll always be screwed, because there will always be more titans for you to kill than there are game turns.
So, in short, you while it's theoretically possible to kill a titan with your dudes, you are absolutely fucked because the cost to do so nets the opponent more titans than you could ever kill.