lol such a nerd topic. but as a qualified nerd myself, ill post first.
First of all, Obi-Wan would've been really stupid to refuse the offer. The jedi would've been wiped out indefinitely. As Windu said, there weren't enough jedi to protect the republic.
As a side note, I don't think it was Obi-Wan that accepted the clones. Palpatine told the senate that he would create an army of the republic and yoda went to Kamino to observe/pick up the clones.