I have to get my top right 2nd molar removed. i already had my wisdom teeth removed so doctor is telling me i need to get the bottom 2 removed too because of chewing purposes. how true is that? he also said something about the bottom molar could shift up

He's correct: Teeth will extrude if there is no opposing tooth. One solution is to remove teeth that have no opposing tooth. Another solution would be to attach lower 2nd and 1st molars together to prevent 2nd molar extrusion. Best alternative may be to replace the upper 2nd molar with an implant/crown.

Need more info: The correct answer to this depends on other variables. How your teeth occlude, the state of your gum health, and what other teeth are missing will have a bearing on the best way to proceed. Sometimes unopposed teeth hyper-erupt and sometimes they don't so there is always an element of uncertainty in predicting complications. This might be a good opportunity to get another opinion. Ask questions.

Replacement ?: Are you going to replace the missing maxillary tooth with an implant? What is the condition of the lower molar? Yes, the lower will super-erupt over time if the maxillary tooth is missing, but no need to extract right now if is healthy. Get a second opinion regarding treatment options.