If you are not prepared to back industrial action due to a dispute over pay and do not think for what ever reason, that being a member of Unite is a good thing, then why should you benefit in any way, if the action carried out by Unite gains an increase from the initial offer of 2%?
It's nothing to do with whether you took part in action or not. It's simply the company cannot discriminate between union and non-union members. In the same way they can't offer a better deal to non-union members as a reward for not taking part in the strike (well, actually, they can offer bonuses for working on strike days, but they can't offer a better ongoing package just because someone is not in the union).