How to set multiple 'active' classes from query string
Perhaps not the most elegant solution, but this works:

{% set queryTags = craft.request.getQuery('tags') %}

{% for tag in craft.tags.relatedTo(resourceTags) %}
   &lt;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 %}"
   &gt;{{ tag.title }}&lt;/a&gt;
{% endfor %}


Adding disabled rather than active.