It DOES have consequences though. If I spec to a tank spec and dont know what I'm doing, word is going to get around that I dont know what I'm doing, and I won't be invited to groups anymore. The community DOES police things like that.
As to your last bit. Kinetic Combat and Infiltration have a lot of the same abilities, making me relatively familiar with how both work (But certainly one would need to practice and study before making the switch though) But the two different abilities ARE NEEDED to play it efficiently. There is enough of a difference to make switching specs necessary, but NOT enough of a difference to justify me playing all of the same content again. But this is just a matter of opinion, not fact.
The fact is, dual specialization and how much it is needed is a matter of opinion. It isn't necessary, and therefore if you don't want it, don't use it. But the game will NOT be worse off for it.