How might they be detrimental? My Korean acquisition is being greatly sped up by it's large number of English and Chinese loan words. Korean grammar is notoriously difficult already even with the loan words. Having 50% of all the new vocabulary be somewhat recognizable makes not only memorization easier, it makes it possible to sometimes understand words I haven't encountered before. It's definitely been a great aid in getting fluent in Korean.

English loanwords in another language might help an English speaking person, no doubt. I was more thinking a Chinese person trying to learn English.

Loanwords tend to pe pronounced quite differently in the host language, which detoriates the accent.