I think the anti-Turner people have a problem with two things, basically:
1) The amount and/or high round of draft picks that will most likely be needed to give up to get him (i.e. a 1st round, or a combo of a 1st and later pick, or just more than one pick, in general). Why give up a 1st or more than one pick when a RB can be taken with only one pick or without sacrificing a 1st?
2) The amount of money that he will have to be paid through a new contact extension: this line of reasoning goes, "Why pay 30 million for Turner when you could draft a rookie for relative chump change and develop him? Both are relative unknown quantities (one with limited NFL experience and the other with none) so why take on an undue financial risk?
/devil's advocate
I can see the logic in both of these objections. I count myself as neither a pro nor anti Turner person. If Marv and Co. through their evaluations think he is the real deal and is the guy that will fit what we want to do on offense, then I would support a trade and extension for Turner, as I don't see Marv and Co. giving up the farm in terms of draft picks for any one player, knowing how much Marv values building through the draft. I will not, however, lose any sleep whatsoever if we pass on Turner and the Titans, for example, mortgage the farm to get him and we instead draft a rookie RB somewhere in the draft. If you think about it, with the idea that Marv values draft picks and is not going to throw a bunch of them to a team to trade for any one player, then we have the situation pretty much under control, as our hand is not forced to move any one way and we can spend our picks and our money where we deem fit.