Use a URL Slug to Search Entries by Tag

Problem

You want to pass a tag to an URL slug to only show entries related to that tag.

Solution

The links:

<ul class="sub-menu">
    {% set allTags = craft.entries.section('blog').limit(null) %}
    {% for tags in craft.tags.relatedTo(allTags) %}
    <li><a href="/templateName/{{ tags.name }}">{{ tags.name }}</a></li>
    {% endfor %}
</ul>

The display template for example.com/templateName/tagName:

{% set searchTag = craft.request.getSegment(2) %}
{% for opinion in craft.entries.section('blog').search(searchTag) %}
{% if opinion is defined %}
...
{% endif %}
{% endfor %}