This is a simple question. If it was G-D that gave us those commandments then there is no problem. However, if it was people who invented those commandments then why would these people invent 613 commandment, most of which ''don't make sense'' and then succeed in making the Jewish people accept them for 3500 years?
For the last time, the people who worship monkeys and cows are the same as those that worship Jesus. They just worship. These people have no commandments and they are free to live their life any way they like, as long as they don't break any laws that might get them in jail.
In that respect, Judaism is different from ALL OTHER monotheistic religions. The definition of monotheism may include the worship of a single G-D but it may also include the worship of a single monkey or a single lunatic who may think and say that he is the son of G-D. Judaism however has Mitzvoth and in that respect there is not a single parallel to it in Man's history.