NATO's primary purpose is deterrence. The stronger the alliance is militarily, the greater the deterrent, and the less chance U.S. troops would ever have to be committed. Realistically, if Russia were to initiate hostilities with NATO, Finland and especially Sweden are very unlikely to be the target, so the chances of adding them being the cause if a war is negligible. The most likely target is one of the Baltic states, so having two more countries with stronger militaries -Sweden - and advantageous geography Finland - is much more likely to deter a war than to cause one.
NATO: Did they or did they not engage in offensive hostilities in say, Iraq? Any other place?