Not trying to start an arguement, but I researched this topic heavily just a few months ago. Yes, typically larger tubes are stonger, but in the case of a scope the difference between 1" and 30 mm is so small that it should not be a decision maker. 30mm tubes, at least Leupold's, use the same internal glass as the 1" tubes. If they used 30mm glass, the would not be able to achieve the extra wind and elev adjustments that make 30mm tubes so poular. Therefor, two identical objective scopes, one 30mm and one 1", have the same light transmission. Where you pick up the better light transmission is through the objective, which is why scopes have evolved from 29-36mm objectives to 40-56 objective.
Don't get me wrong, I'm not saying don't buy a 30mm, I have several and I like them, just buy them for the right reason...increased range of adjustment