Instead of making 2 into 1 when you decrease, try making 3 into 1 (a double decrease). This should allow you to stay in rib. E.g., if you use p3tog (to bring together a P, a K, and a P), the new P will still have K's on each side so the rib pattern will be maintained. Remember to take into account that each decrease will reduce your stitch count by 2 when you do your calculations.
There is no right way to knit; there is no wrong way to knit. So if anybody kindly tells you that what you are doing is "wrong," don't take umbrage; they mean well. Smile submissively, and listen, keeping your disagreement on an entirely mental level. They may be right, in this particular case, and even if not, they may drop off pieces of information which will come in very handy if you file them away carefully in your brain for future reference.