Bullshit. Most enlistment contracts specify a particular career field. The troops in combat arms are there because they chose that option. The Pentagon isn't going to take a dental assistant and reassign them to infantry unless they specifically request that change (and meet various eligibility criteria).
Your contract specified that you wouldn’t be sent to a war zone? I don’t believe that. You might be able to find a job that’s unlikely to get you deployed.
If the US military starts wantonly changing enlistment contracts, we aren't that far from a national draft anyway, so the distinction is kind of meaningless.