It's Not Immoral, Just Dumb
Sure, it happens sometimes. But I'm not a big supporter of this type of bachelor party. Not because I think it's immoral. I just think it's dumb.
If You Can't Be Good, At Least Be Safe
First of all - let me guess - I bet the men who are being "serviced" don't wear condoms. Smart move! Professional sex workers are at a very high risk for HIV, syphilis, genital warts and more. Much more. (Some of these diseases can be passed orally, by the way.) So boys, do yourself and your friends - they ARE your friends aren't they? - a favor and take some Trojans to the next party.
Second, I think the original idea behind the bachelor party was to get some sexual experience for the na¬ve or virginal groom or to have one last "fling" before being "tied down" to a life of drudgery in marriage. However, as you point out, most grooms are not so na¬ve at marriage - they've had plenty of flings.
The part I like least is the assumption that marriage will be the end of the man's sex life. Yet for many, it is the beginning of a truly exciting and satisfying sex life. (Many, many men I know had very dull sex lives before marriage.) So why is the night of debauchery necessary?
There is one exception. There are a few people for whom strippers, sex workers, and other sexual experimentation is an integral part of their relationship.
In these cases, both partners may want to have bachelor parties - alone or together. If this is their agreement, it could work. But these people are usually smart enough to wear condoms.