On the specific issue of harm, remember that a person reviewing a resume may only have 15-20 seconds to review your resume before deciding whether to toss it in the “No” pile or the “Maybe” pile.
If you make the “Maybe” pile, then your resume will get a longer more detailed read—perhaps a full minute. From here, your resume will again be sorted into either the “No” pile or the “Maybe” pile.
If you make this second “Maybe” pile, then you will likely be called for an interview.
If you have something on your resume that is deemed old, it probably depends upon where it is on your resume.
If the old technology is listed say at the top of your resume, in a bulleted list of keywords, then it could be extra “fluff” reading that increases your chances of going into the “No” pile.
If the old technology is listed in the chronological portion of your resume, back when you worked for WidgetMaster Inc. in the mid 1990s, then it could actually be helpful since it shows the technology you were using in that position. Consistent use of technology keywords under each employer can show a progression of skills.