Perhaps not the most elegant solution, but this works:
{% set queryTags = craft.request.getQuery('tags') %}
{% for tag in craft.tags.relatedTo(resourceTags) %}
<a
href="{% if tags == "" %}/learning/resources?tags={{ tag.title|kebab }}{% else %}/learning/resources?tags={{ tags|replace(' ', '+') }}+{{ tag.title|kebab }}{% endif %}"
class="btn btn-default{% if tag.title|kebab in queryTags %} disabled{% endif %}"
>{{ tag.title }}</a>
{% endfor %}
Adding disabled rather than active.
