If I had been hired as a DEC at their former carrier when they were an FO, and the company then prevented them from upgrading, they'd feel the same way. And I would be buying lunch and drinks on trips for them as a peace offering. Your situation with the lifer CAs is apples and oranges. They are senior to you at this company, ergo they hold CA slots while you wait your turn. I have no problems with pilots senior to me holding CA slots. That's the way it's supposed to work, as we've all been told since we started working to get into this industry.

Seniority with your current company is the system we work under. There is no national seniority list, so DECs are viewed as cutting ahead in line. When a company hires DECs rather than upgrading its existing FOs in seniority order, and then refuses to set things right afterwards, it creates bitterness among the pilot group. Mostly, the bitterness is directed at management for creating the mess in the first place. I've flown with several of the DECs on the Saab, great guys to work with. I can only speak for myself, but my feelings are nothing personal against them.