It would've ended up in a fight regardless. Shinkurou himself doesn't look like much, stated by Ginko in this episode that he doesn't look strong. If you and two of your friends were with you, and some faggot comes up and tells you what to do, will you listen? Maybe, but you have to remember that these 3 guys are assholes.
Shinkurou did the right thing, like >>11086527
stated, it would've had the opposite effect if he got into a fight with them. What if those same guys, after getting their asses kicked, finds Murasaki who left the apartment again, alone?