Given that steam engines were running in an era with very different safety regulations and liability laws , that they may want to use a freight engine hauling passenger cars where a diesel can easily provide things like auxiliary power and the like (especially if it is an engine set up for passenger service), or simply to give the engine more of a safety margin than it would have alone, it makes sense. Doesn't change the fact the engine is leading the train to me, it just seems like a great way to be able to see the engine run at all, and that is the important point. Could a big boy pull a train without help? Sure, passenger or steam, it could, but the real question is does it make sense to do that, if you can do better with a helper diesel,why not?
As far as the negative reactions to the Big Boy project, from experience with other similar things, some of it likely is personal, not liking the people doing the project (not liking that the UP is doing it cause they don't like the UP, don't like the person heading it, don't like big companies doing something for PR, etc).
In other cases it can be jealousy of a sorts, where in this case a big company with large resources makes a big fanfare restoring a famous engine and get huge publicity for it, meanwhile a lot of volunteer groups across the country have been saving engines from the scrap heap and bringing them back to life, scrambling to raise money to do it, trying to find places to be able to run them (and often it is big railroads, like CSX and NS, basically pulling the rug out from groups wishing to use their rails to run excursions),otherwise breaking their humps doing it, out of love, and being overshadowed by this big event done for corporate PR, I can understand that. Call it the NY Yankee syndrome as well, where fans of other teams complain that it is no big deal to win as a Yankee, they buy championships, so no one should make a big deal when they win, that the real feat is winning with a small market team with a lot of clever personnel moves, team spirt, etc - some of which is true, some of which is based on sour grapes, given that the Yankees in the free market era have often had decades of horrible teams when they spent the most money). And as a disclaimer, this is not aimed at anyone who has posted on here, this is based on a lot of years observing similar things and applying it here.
