I don't think being "soft" means you cant play Oline. There are quite a few OL men out there who are nice and big teddy bear type guys like gross and kalil. The key is to being a good offensive lineman is a combination of technical skills and having the right weight/size/power to be able utilize those technical skills correctly.
Bottom line is you shouldn't discount Martin because he is overly emotional and you view him as weak person. Make the the business decision (no emotions involved).
He is cheap
He fills a huge need
He has potential to improve the team (When your drafting players your gambling on their potential to be great. This is no different)
Let it go dude. He cant play. You're also confusing being nice with being soft. Gross and Kalil are nice, but will get up in you given the opportunity.