It's not ridiculous, it's more realistic, and it adds more replay value. If your going to throw a statement out there that the amount of people who replay games is minuscule your gonna have to have something to back that up. I don't believe that for a single second. Fallout is meant to played more than once, or...at least...previous Fallout games have been, this one...not so much. People who play these sorts of game tend to play them more than once, if the content is there for them to do so.
People join every single faction in Bethesda games because they know the games are going to let them do it, no matter how silly it seems. If they know that there is a possibility that one faction could mean not being able to join another one, then they are going to be more informed about their decisions, so if they meet the Brotherhood first, find out that they are absolutely gung ho about killing all mutans, ghouls, and synths, they might say no thanks at first. Also, I already said joining the Minutemen and one of the others is fine, just not the Brotherhood and the Railroad.
The various people in this game seem pretty danged good at knowing what your doing when your working with one of the other factions. Maxson even knows that you give away the thing you get from the Institute if you give it to someone else. I built the transporter, copied all their info, came back and gave it to Sturges, and Maxson somehow knew about it. So it's really not a stretch to me for him to know if I help Synths.
I never once felt herded towards meeting Danse at all on my way to DC, and I did that fairly early in the game. I saw a radio signal, listened to it and I thought, "Huh, I'll have to check that out at some point", and went on my way. I did feel herded towards Concord yes, but I didn't even feel herded towards DC let alone meeting Danse.
More than possible does not equal likely, at all. It just means that it is very possible to happen. Oh, and you can meet all of the factions before you join any of them. Not a single one of them says, if you don't join at that moment in time, then you can never join at all. I'd imagine even that if you tell Desdemona that you would not kill to save a synth, you can go back later and change your mind about that.
This game is just not written very well at all. They tried to make being able to join everything make sense, but they just didn't pull it off.
Man...I want windows...that was one of the things that annoyed me the most with the building.