Personally I wish Labour would drop Trident, but it seems to me that any future Labour government that wished to keep it could ask for support from the Tory opposition for that purpose, making SNP support on the issue unnecessary. Obviously the Tories could sit on their hands, but even if they abstained that would very likely be enough for Labour to get its bill to renew Trident through. Or would the Tories want to be seen walking through the lobbies to vote against the UK's nuclear deterrent, merely for reasons of party advantage? I don't think that would play very well in any subsequent election.
In other words, I don't see what the fuss is about. Have I missed something?