REA is probably not harmful if you’re really a qualified applicant, but whether it helps at all would likely depend on how unique your ECs are. If they are average (this includes if you have heavy involvement but nothing that would be rare among applicants) it won’t make a difference because that aspect of your app won’t significantly help get you in anyway. On the other hand, if you’re really so unique that you’re sure no other candidate can provide what you have to offer, then that unique quality will be an equally big boost regardless, as you’d be the first person like yourself they see either way.
The scenario in which REA might actually help would be if you’re fairly special at something but definitely not truly unique among applicants. For example, if you’re a nationally recognized tuba player, if you’re lucky enough Stanford might actually need a tuba player for their band that year, making you a much more attractive applicant. In that case EA would help because they might just take the first applicant who fits that need, whereas if you apply RD they might have already filled their tuba need with a slightly less accomplished tuba player who applied EA. In contrast, if you founded a new scientific field that seriously advances humankind, you don’t have much danger of someone else being able to fill that need, so you’ll get that boost no matter when you apply.