They will often not want to go to the trouble of going back and forth with the contract and will just accept it.
Pretty sure you don't have to tell them if you return the contract to them modified and they sign it. They weren't going to tell you all the objectionable parts of the contract, so why give them information you're not required to give?
(IANAL)
You want everything to be as clear as possible, and with no obvious points that can be called into doubt. Even if you end up winning, you don't want a court case that drags out for multiple years, with devastating legal costs to cover while its going on.
Some of the docu-sign sites even have tools for this.. others don't.