If players were allowed to be anywhere on the field, you would always have attackers far down the field, which would mean defenders would always play back, which means you don't get the very thing you're looking for by getting rid of offsides.

Offsides allows defenses to push up, but this creates space behind them that helps with fast breaking counters.

I love these people who know nothing about the sport, but think they can "fix" it by getting rid of offsides. Thanks for your stellar input.