When giving an argument for having to complete a task or assignment, the words "have to" are not sufficient. There is always a reason that could be given for doing a task. It could even be that it is the way the boss wants it completed, or you believe that it will benefit the customer. Have To is not adaquate enough.
Saying "have to" does not feel like a weasel word argument. It stresses the persons belief on the subject which is fine, without actually forcing someone into thinking their way. It lays importance on a subject, but it seems like a normal way of talking than a weasel word type of argument.