It's the unpopular part of the law. But pretty much anything that works is going to have some unpopular component that needs to be swallowed in order for the whole thing to work.
When Republicans talk about getting rid of the individual mandate, it's because they are, in actuality, trying to kill the law. When Democrats talk about it, I really don't know what's going through their heads. Leftist wonks like Krugman or Klein keep on telling them exactly why it's needed.
I don't see how it would be, unless by "subtracting individual mandate" you mean "replacing an individual mandate backed with a fee/tax/penalty for failure to comply with a universal tax, an option to select a private option with the tax refunded as a subsidy, and a default of using the public option if no private option is selected". Which, really, is retaining the individual mandate, but making it impossible to break rather than penalizing breaking it.